Boost prep a Nikki (how to)
04-02-15, 11:04 PM
#76
carb whisperer
little bit smaller primaries wouldnt hurt, but dont get carried away with the numbers. Sometimes you just gotta give the engine what it wants. My car wont happily transition from cruising at 13
One of the reasons the Holley is going.
Another thing I noticed today. The Nikki has transfer slots like the Holley does. For the primaries, i think your lean spot could be finished off with leaner jets and a bigger pump shot, but the secondary delay could be helped by some higher fuel flow through the last restriction in the transfer circuit. There are "slots" above the secondary throttle blades while closed, but they dont extend below it. If you could somehow extend them to just slightly past the blades, youd already have fuel flow in the circuit while they are closed.
This would greatly affect your jetting, but you wouldnt have to worry about waiting for the secondary main circuit to come online if its already partially in motion before you drop the hammer....
One of the reasons the Holley is going.
Another thing I noticed today. The Nikki has transfer slots like the Holley does. For the primaries, i think your lean spot could be finished off with leaner jets and a bigger pump shot, but the secondary delay could be helped by some higher fuel flow through the last restriction in the transfer circuit. There are "slots" above the secondary throttle blades while closed, but they dont extend below it. If you could somehow extend them to just slightly past the blades, youd already have fuel flow in the circuit while they are closed.
This would greatly affect your jetting, but you wouldnt have to worry about waiting for the secondary main circuit to come online if its already partially in motion before you drop the hammer....
Last edited by wankel=awesome; 04-02-15 at 11:15 PM.
04-02-15, 11:40 PM
#77
This carb is running better than it ever has. More grunt, more drivability, more power, breaking them loose in 1st and 2nd is child's play now (no tricks necessary such as reving to dump the clutch or punching it through a corner). You just flex your ankle from any RPM and wait for the boost to spool up which is a new experience for me. You don't have to wait that long.
I guess what I'm saying is maybe I should just give it what it wants? It seems to like the current tune. I'm thinking if I were to lean out the primaries to get to 13 it would increase the secondary delay due to having less already atomized fuel available. Seems kinda similar to trying in vain to get rid of the 1500 lean spot I spent several hours on earlier today. Turned out once I drove it, the lean spot wasn't even there.
And when I did notice it, it was little more than a split second glitch which felt a lot like an accel pump, and even then it wasn't like your typical accel pump problem youd get right off idle. I'm probably not explaining it very well but it acts like a random lean glitch. It's random so you never know which time you hit the pedal it will do it, but I've gotten better at predicting it. In other words, it's not a problem.
As for the secondaries, I might try solder filling some jets I'll never use and drill to 80 and maybe drill another set to 135 for fuel. Sounds really small but the current 140s at 10.0 on the wideband.
As for the slots you speak of, I think they communicate with the slow bleeds and thus would be useless because mine are solder filled. Not sure. I'd have to take a look at how they're plumbed.
I guess what I'm saying is maybe I should just give it what it wants? It seems to like the current tune. I'm thinking if I were to lean out the primaries to get to 13 it would increase the secondary delay due to having less already atomized fuel available. Seems kinda similar to trying in vain to get rid of the 1500 lean spot I spent several hours on earlier today. Turned out once I drove it, the lean spot wasn't even there.
And when I did notice it, it was little more than a split second glitch which felt a lot like an accel pump, and even then it wasn't like your typical accel pump problem youd get right off idle. I'm probably not explaining it very well but it acts like a random lean glitch. It's random so you never know which time you hit the pedal it will do it, but I've gotten better at predicting it. In other words, it's not a problem.As for the secondaries, I might try solder filling some jets I'll never use and drill to 80 and maybe drill another set to 135 for fuel. Sounds really small but the current 140s at 10.0 on the wideband.
As for the slots you speak of, I think they communicate with the slow bleeds and thus would be useless because mine are solder filled. Not sure. I'd have to take a look at how they're plumbed.
04-03-15, 12:49 PM
#78
carb whisperer
Progress on my own.
24.5 mm primaries, 16* inlet angles, 26mm secondaries, 16* inlet angle
122 primary main fuel jet. 170 secondary main fuel jet (i had a pair so just threw them in)
70 primary air bleeds, 120 secondary air bleeds. 40 long slow bleeds on the primary. No idea what the secondary is. Whatever stock was.
Drilled 118 nickel plated 60's primary slow air bleed, stock nickel plated 60 secondary (for now)
Mech secondary, custom thick throttle body gasket, and 6 accel pump "spaceer" gaskets.
1 1/4" spaced pump arm extension on the linkage.
Anything im forgetting?
Last edited by wankel=awesome; 04-03-15 at 12:57 PM.
04-03-15, 07:10 PM
#82
Wow, nice work! Manly tears of joy are being shed over here lol.
A couple of pointers. Looks like your primary long slows are 46, not 40. Notice
the number stamp is a little off but it looks like a 6. Did you get a chance to poke
a .40mm drill bit or anything else around that size into the tapered end? As an
example my stock 42s will not let a .42mm drill bit in, but the 46s do. The drill bit
starts to get stuck just in the end so I didn't force it.
I noticed your secondary main air bleeds are 120. This is a good starting place
for boost. Try test fitting your 118 drill bit in them and I bet it will get stuck or
won't go in at all. But for now running it NA should be fine, or swap in some 140s
if the secondaries are too rich. I think leaving the secondary slows fully open and
stock is fine, along with the 170 jets. Of course some tuning is in order. Knowing
you, you will want to tune this carb!
As for your primary side, it all looks good as a starting point for boost but you
may want to up your primary jets a tiny bit for NA. I had good luck going to
factory 130s (around 1.27mm) back when I had 90 air bleeds. Note: I have had
success with 60 air bleeds and 118 fuel jets but it still seemed a little lean.
Anyway I think your carb is set up well enough that it will start up and run NA so
some fine tuning can begin.
As for the rest of the carb, it all looks good. I like the thick baseplate gasket and
the accel pump mods. Do I see some polished metal here and there?
Oh did you drill out the banjo bolt to 118 or whatever size you decided on? Or
going to leave it stock? And I know you have ideas about the nozzle ie leaving
them stock for a longer pump shot duration. That might not work this way seeing
as there is a 30 air bleed above the steel ball and small brass weigh that lets out
over-pressure back into the float bowl or it's an anti-siphon to prevent accel
pump fuel from being pulled out at high RPM like the Holleys need on the
secondary accel pump. But then this is a primary accel pump. Meh, too much
speculation. Better to throw some gas in it and see what it does.
A couple of pointers. Looks like your primary long slows are 46, not 40. Notice
the number stamp is a little off but it looks like a 6. Did you get a chance to poke
a .40mm drill bit or anything else around that size into the tapered end? As an
example my stock 42s will not let a .42mm drill bit in, but the 46s do. The drill bit
starts to get stuck just in the end so I didn't force it.
I noticed your secondary main air bleeds are 120. This is a good starting place
for boost. Try test fitting your 118 drill bit in them and I bet it will get stuck or
won't go in at all. But for now running it NA should be fine, or swap in some 140s
if the secondaries are too rich. I think leaving the secondary slows fully open and
stock is fine, along with the 170 jets. Of course some tuning is in order. Knowing
you, you will want to tune this carb!
As for your primary side, it all looks good as a starting point for boost but you
may want to up your primary jets a tiny bit for NA. I had good luck going to
factory 130s (around 1.27mm) back when I had 90 air bleeds. Note: I have had
success with 60 air bleeds and 118 fuel jets but it still seemed a little lean.
Anyway I think your carb is set up well enough that it will start up and run NA so
some fine tuning can begin.
As for the rest of the carb, it all looks good. I like the thick baseplate gasket and
the accel pump mods. Do I see some polished metal here and there?
Oh did you drill out the banjo bolt to 118 or whatever size you decided on? Or
going to leave it stock? And I know you have ideas about the nozzle ie leaving
them stock for a longer pump shot duration. That might not work this way seeing
as there is a 30 air bleed above the steel ball and small brass weigh that lets out
over-pressure back into the float bowl or it's an anti-siphon to prevent accel
pump fuel from being pulled out at high RPM like the Holleys need on the
secondary accel pump. But then this is a primary accel pump. Meh, too much
speculation. Better to throw some gas in it and see what it does.
Last edited by Jeff20B; 04-03-15 at 07:37 PM.
04-03-15, 07:36 PM
#83
The secondary delay
So I think I know why I still have a secondary delay sometimes and then other
times it's gone. It's due to a leaky brake booster.
The rear rotor used to run lean due to the excess incoming air coming in on the
secondary runner. I didn't want to deal with swapping in a new brake booster so
I drilled and tapped the intake manifold on the front secondary runner to let a bit
of brake booster air in. I also added a bit of weld to the banjo bolt holes. This
worked great as a band-aid fix for an NA. You just adjust the mixture screw a
little to compensate for the air and it ran great. No more lean rear rotor!
Now that I'm boosting, this leaking brake booster is a bit of a problem. But I
have another band-aid fix. It is a one way valve from an old school rotary like a
Cosmo or RX-3. This will continue to let the brake booster air come into the
manifold but as soon as boost hits, the valve inside closes and it seals really
well. So I'll add it right after the two hoses Tee together.
Yes, I know the correct fix is a new brake booster. I'll get one when the master
cylinder needs work.
Earlier today I filled a set of unneeded jets with solder and drilled out to .72mm.
Then after I was done the thing about the brake booster suddenly hit me and I
was like of course! That explains everything! See, the reason why the delay
happens some of the time but not all the time is due to how pressurized the
entire brake booster hardline AND the booster itself is. When there is no more
vacuum in the entire system, such as when the primaries are providing a little bit
of boost (showing 0 on the vac/boost gauge or when the turbo is making as
much air as the engine is ingesting), there is no delay. The only way this can
happen with any consistency is usually in 3rd gear because it's taller and takes
longer for the RPMs to climb. Or to put it another way more time has passed
since the last upshift compared with 1st that whizzes by quickly, to 2nd which
still whizzes by pretty quickly, to 3rd which actually puts a nice load on the turbo
and makes it spool up faster thus providing more boost over a longer period of
time, and totally fills the brake booster so the entire flow of air through the
vacuum tube hardline has reversed direction and is in positive territory. That
sentence was way too long, wasn't it? Anyway the tendency for there to be too
much unwanted air and not enough fuel in the secondary runners of my intake
manifold is less likely in 3rd gear than the first two gears.
Something tells me no amount of tiny secondary air bleeds will make the delay
go away completely because the problem is not in the carb. It's in the car. It's
always been there. When I first started driving it I recall seeing orange dust
inside the banjo bolt and the hardline fitting in the manifold. I bet that was nice
for the engine to suck in. Well, it only lasted a few miles and hasn't been noticed
since.
The point of all this is don't worry about a horrible unsolveable secondary delay
from your boosted Nikki. Unless you have a leaking brake booster, but then
you'd probably know about it by now. It makes a hissing sound for a few
seconds after you shut it off. I asked j9fd3s whether this was normal on the 84-
85 for any reason and he said NO! I asked because PercentSevenC's red car did
the exact same thing, but it stopped hissing a few seconds sooner than mine. I
guess my leak is bigger?
Anyway I think with your 120 secondary air bleeds and solder filled slows, you
should not have a delay at all. But if you do it is probably a matter of slightly
smaller main air bleeds.
One more thing. Back when I was doing NA testing with a stock accel pump and
hogged venturis, it had a split second delay. All the secondary air bleeds were
entirely stock (140 mains). I did the accel pump mod and the delay went away.
times it's gone. It's due to a leaky brake booster.
The rear rotor used to run lean due to the excess incoming air coming in on the
secondary runner. I didn't want to deal with swapping in a new brake booster so
I drilled and tapped the intake manifold on the front secondary runner to let a bit
of brake booster air in. I also added a bit of weld to the banjo bolt holes. This
worked great as a band-aid fix for an NA. You just adjust the mixture screw a
little to compensate for the air and it ran great. No more lean rear rotor!
Now that I'm boosting, this leaking brake booster is a bit of a problem. But I
have another band-aid fix. It is a one way valve from an old school rotary like a
Cosmo or RX-3. This will continue to let the brake booster air come into the
manifold but as soon as boost hits, the valve inside closes and it seals really
well.
So I'll add it right after the two hoses Tee together.Yes, I know the correct fix is a new brake booster. I'll get one when the master
cylinder needs work.
Earlier today I filled a set of unneeded jets with solder and drilled out to .72mm.
Then after I was done the thing about the brake booster suddenly hit me and I
was like of course! That explains everything! See, the reason why the delay
happens some of the time but not all the time is due to how pressurized the
entire brake booster hardline AND the booster itself is. When there is no more
vacuum in the entire system, such as when the primaries are providing a little bit
of boost (showing 0 on the vac/boost gauge or when the turbo is making as
much air as the engine is ingesting), there is no delay. The only way this can
happen with any consistency is usually in 3rd gear because it's taller and takes
longer for the RPMs to climb. Or to put it another way more time has passed
since the last upshift compared with 1st that whizzes by quickly, to 2nd which
still whizzes by pretty quickly, to 3rd which actually puts a nice load on the turbo
and makes it spool up faster thus providing more boost over a longer period of
time, and totally fills the brake booster so the entire flow of air through the
vacuum tube hardline has reversed direction and is in positive territory. That
sentence was way too long, wasn't it? Anyway the tendency for there to be too
much unwanted air and not enough fuel in the secondary runners of my intake
manifold is less likely in 3rd gear than the first two gears.
Something tells me no amount of tiny secondary air bleeds will make the delay
go away completely because the problem is not in the carb. It's in the car. It's
always been there. When I first started driving it I recall seeing orange dust
inside the banjo bolt and the hardline fitting in the manifold. I bet that was nice
for the engine to suck in. Well, it only lasted a few miles and hasn't been noticed
since.
The point of all this is don't worry about a horrible unsolveable secondary delay
from your boosted Nikki. Unless you have a leaking brake booster, but then
you'd probably know about it by now. It makes a hissing sound for a few
seconds after you shut it off. I asked j9fd3s whether this was normal on the 84-
85 for any reason and he said NO! I asked because PercentSevenC's red car did
the exact same thing, but it stopped hissing a few seconds sooner than mine. I
guess my leak is bigger?
Anyway I think with your 120 secondary air bleeds and solder filled slows, you
should not have a delay at all. But if you do it is probably a matter of slightly
smaller main air bleeds.
One more thing. Back when I was doing NA testing with a stock accel pump and
hogged venturis, it had a split second delay. All the secondary air bleeds were
entirely stock (140 mains). I did the accel pump mod and the delay went away.
04-03-15, 11:23 PM
#85
Good man!
Update time!
The anti-delay device worked!
No more delay in 2nd and 3rd! But what about 1st gear you ask? I tried it twice
under different conditions with different results. The first time it had a delay or
rather a bog, I think from too low of an RPM. This is something any mechanical
secondary carb will experience. The second time was just going up a short hill
nearby because I was getting low and gas and didn't want to push my luck. It
didn't delay or bog this time! I think I solved it! Finally!
Update time!
The anti-delay device worked!
No more delay in 2nd and 3rd! But what about 1st gear you ask? I tried it twice
under different conditions with different results. The first time it had a delay or
rather a bog, I think from too low of an RPM. This is something any mechanical
secondary carb will experience. The second time was just going up a short hill
nearby because I was getting low and gas and didn't want to push my luck. It
didn't delay or bog this time! I think I solved it! Finally!
04-04-15, 10:23 PM
#86
As usual something wankel=awesome said, or rather did, inspired me in some
way. This time it was his '76 carb all hogged out and boost prepped but tuned
for NA. I have a 79 carb hogged out and boost prepped, also tuned for NA but I
decided to try it with boost. I'll cut to the results followed by the tune and my
speculations for how to improve it. This could be valuable to anyone with an SA
carb or older.
Results: Idle is easily adjusted thanks to having an AIR screw along with a
fuel screw. Made my life easier. It has the usual 1500 to 2000 lean spot of a
hogged out Nikki but it was not noticed at all while driving. You can find it if you
concentrate and keep your foot really steady while watching the wideband. At
part throttel cruise it ran a little leanish for my taste at 13 AFR but got really
scary lean (17) as I'd get on it until the secondaries opened at which point it
goes to 10.0 and breaks them loose easily with no delay.
Tune:
pri air: 90
pri fuel: 118
sec air: 92
sec fuel: 137
pri short slow: 118
pri long slow: 45
sec short slow: solder filled
sec long slow: solder filled
accel pump mod: 6 gaskets and 1 1/4" extension
118 drilled banjo bolt and nozzles
Speculation for improvement:
1) Float level.
At first this carb would flood itself out agressively due to new needles and seats.
Swapped the floats as it turned out the previous owner mangled the part you're
not supposed to bend. Found a set of unmolested ones and had to tweak one a
tiny bit to get them even. Turned out the float level is a little low but I left it there
as the needles and seats burnish together. I'll raise it to the middle of the
windows after some miles. It should also raise slightly on its own as they break
in more.
2)Limited boost signal getting to the float bowls.
The PO installed some small brass tubes in the float bowl vent channels held in
place by quicksteel as a racing mod to prevent slosh I think. It seems to slow
down the boost signal entering the float bowls so it's kinda doing what we don't
want. I'll dig it all out at some point.
3)118 primary fuel jets.
So far I think the carb needs 122s so I'll just drill them out next time I get a
chance.
4)90 air bleeds.
These are stock for 79 carbs and probably aren't the problem but they do make
the primary fuel jets seem small and insignificant. I'm still thinking with 70 air
bleeds on the brain becaue that's what most FB carbs come with. This is the first
SA carb I've ever tuned for boost so this is all kinda new for me.
5)Calibrated boost leak.
Do any of you remember last year when I had to add a calibrated boost leak to
the line between the Mallory fpr and the carb hat? I added it because the Mallory
is really sensitive to anything above atmostpheric whenever the turbo would
spin up. It pushed too much fuel into the Nikki and caused flooding issues when
driving spiritedly in vacuum. The carb didn't need this much fuel for this kind of
driving so I added about a 1.00mm air leak inline. It fixed the problem. I noticed
some carbs needed a smaller hole more around .65mm. Perhaps maybe this '79
carb needs less leak or no leak at all. The only way to find out is to remove the
leak and see.
Of course I also corrected my fuel system since then with a proper 5/16" send
and 3/8" return, which has helped in other ways (basically no more flooding
unless I boost for a second and let off). I left the leak because it didn't seem to
cause any problems with any of the FB carbs but I realize the primary choke
opening of the SA carbs is a lot bigger so maybe that has something to do with
it. Maybe the SA carb offers less restriction to the incoming boosted air and less
goes to the mallory before it's needed.
What do you guys think?
way. This time it was his '76 carb all hogged out and boost prepped but tuned
for NA. I have a 79 carb hogged out and boost prepped, also tuned for NA but I
decided to try it with boost. I'll cut to the results followed by the tune and my
speculations for how to improve it. This could be valuable to anyone with an SA
carb or older.
Results: Idle is easily adjusted thanks to having an AIR screw along with a
fuel screw. Made my life easier. It has the usual 1500 to 2000 lean spot of a
hogged out Nikki but it was not noticed at all while driving.
You can find it if you concentrate and keep your foot really steady while watching the wideband. At
part throttel cruise it ran a little leanish for my taste at 13 AFR but got really
scary lean (17) as I'd get on it until the secondaries opened at which point it
goes to 10.0 and breaks them loose easily with no delay.
Tune:
pri air: 90
pri fuel: 118
sec air: 92
sec fuel: 137
pri short slow: 118
pri long slow: 45
sec short slow: solder filled
sec long slow: solder filled
accel pump mod: 6 gaskets and 1 1/4" extension
118 drilled banjo bolt and nozzles
Speculation for improvement:
1) Float level.
At first this carb would flood itself out agressively due to new needles and seats.
Swapped the floats as it turned out the previous owner mangled the part you're
not supposed to bend. Found a set of unmolested ones and had to tweak one a
tiny bit to get them even. Turned out the float level is a little low but I left it there
as the needles and seats burnish together. I'll raise it to the middle of the
windows after some miles. It should also raise slightly on its own as they break
in more.
2)Limited boost signal getting to the float bowls.
The PO installed some small brass tubes in the float bowl vent channels held in
place by quicksteel as a racing mod to prevent slosh I think. It seems to slow
down the boost signal entering the float bowls so it's kinda doing what we don't
want. I'll dig it all out at some point.
3)118 primary fuel jets.
So far I think the carb needs 122s so I'll just drill them out next time I get a
chance.
4)90 air bleeds.
These are stock for 79 carbs and probably aren't the problem but they do make
the primary fuel jets seem small and insignificant. I'm still thinking with 70 air
bleeds on the brain becaue that's what most FB carbs come with. This is the first
SA carb I've ever tuned for boost so this is all kinda new for me.
5)Calibrated boost leak.
Do any of you remember last year when I had to add a calibrated boost leak to
the line between the Mallory fpr and the carb hat? I added it because the Mallory
is really sensitive to anything above atmostpheric whenever the turbo would
spin up. It pushed too much fuel into the Nikki and caused flooding issues when
driving spiritedly in vacuum. The carb didn't need this much fuel for this kind of
driving so I added about a 1.00mm air leak inline. It fixed the problem. I noticed
some carbs needed a smaller hole more around .65mm. Perhaps maybe this '79
carb needs less leak or no leak at all. The only way to find out is to remove the
leak and see.
Of course I also corrected my fuel system since then with a proper 5/16" send
and 3/8" return, which has helped in other ways (basically no more flooding
unless I boost for a second and let off). I left the leak because it didn't seem to
cause any problems with any of the FB carbs but I realize the primary choke
opening of the SA carbs is a lot bigger so maybe that has something to do with
it. Maybe the SA carb offers less restriction to the incoming boosted air and less
goes to the mallory before it's needed.
What do you guys think?
Last edited by Jeff20B; 04-04-15 at 10:51 PM.
04-06-15, 07:41 PM
#87
carb whisperer
Got mine installed and running well.
The throttle response is insane, and somehow its running near perfect with no real tuning.
I hooked the wideband to it and im seeing 14.0:1 cruising, and 13.2-12.5:1 at WOT depending on gear.
Mine idles happily at 12.5:1 as well.
Only complaints is the idle speed, at 950 RPM, and the feeling that my secondaries are sticking.
I cant tell if its vacuum thats holding them closed, but its a clear force to open the secondaries up.
Mine does have a slight bog if you try to floor them open too early, but its extremely insignificant.
I also have the lean spot from 1.5k RPM to 2k on the primary tip in. Its barely noticeable.
I think slightly smaller slow air bleeds will clean mine up to where I wont even feel it.
Now to start building these for sale.... Should be easy as im used to building and tuning the 100x more difficult to tune Holley's
The throttle response is insane, and somehow its running near perfect with no real tuning.
I hooked the wideband to it and im seeing 14.0:1 cruising, and 13.2-12.5:1 at WOT depending on gear.
Mine idles happily at 12.5:1 as well.
Only complaints is the idle speed, at 950 RPM, and the feeling that my secondaries are sticking.
I cant tell if its vacuum thats holding them closed, but its a clear force to open the secondaries up.
Mine does have a slight bog if you try to floor them open too early, but its extremely insignificant.
I also have the lean spot from 1.5k RPM to 2k on the primary tip in. Its barely noticeable.
I think slightly smaller slow air bleeds will clean mine up to where I wont even feel it.
Now to start building these for sale.... Should be easy as im used to building and tuning the 100x more difficult to tune Holley's
04-06-15, 10:44 PM
#88
Congrats!
It's nice to see someone else having success with these carbs.
You followed my tuning advice. Could that be why it's tuned pretty well right
out of the box? Or are you pulling my leg?
Hmm, 14.0 at cruise sounds lean to me, but then I have a turbo and a ported
13B asking for a lot more air at the same RPM as you.
Nice idle AFR. Question: how much air and fuel screw threads do you have
available for tuning the idle? Like are both screws almost all the way in or are
they several turns out in a normal range?
What about the idle speed at 950? Does it not go any lower? Are you wanting it
to go lower? Does it vibrate? I don't understand.
Are the secondaries easier to open when the engine isn't running? Maybe the
way you tied them together is causing a bind? And yes vacuum does help hold
them closed to some extend. It's due to the way the blade is offset in the shaft.
Yep, typical mech secondary behavior. You gotta love it!
Ah, the 1500 to 2000 lean spot. Glad it's so small on your carb.
Don't go too small on the slow air bleeds.
Be my guest! Youll find after about six carbs that you want to stop. lol You'll go
stir craz- no you'll go Sterling Crazy! Kinda like he did.
It's nice to see someone else having success with these carbs.
You followed my tuning advice.
Could that be why it's tuned pretty well right out of the box? Or are you pulling my leg?
Hmm, 14.0 at cruise sounds lean to me, but then I have a turbo and a ported
13B asking for a lot more air at the same RPM as you.
Nice idle AFR. Question: how much air and fuel screw threads do you have
available for tuning the idle? Like are both screws almost all the way in or are
they several turns out in a normal range?
What about the idle speed at 950? Does it not go any lower? Are you wanting it
to go lower? Does it vibrate? I don't understand.
Are the secondaries easier to open when the engine isn't running? Maybe the
way you tied them together is causing a bind? And yes vacuum does help hold
them closed to some extend. It's due to the way the blade is offset in the shaft.
Yep, typical mech secondary behavior. You gotta love it!
Ah, the 1500 to 2000 lean spot. Glad it's so small on your carb.
Don't go too small on the slow air bleeds.
Be my guest! Youll find after about six carbs that you want to stop. lol You'll go
stir craz- no you'll go Sterling Crazy! Kinda like he did.
04-06-15, 11:14 PM
#89
Racing Nikki
So I test ran the racing Nikki today with a 1980 top, that used to have the spring
loaded rods like your carb, which I've since abolished. I installed a set of new
needles and seats and needed to make sure the fuel level would be in the
middle of the windows. After some semi-floodiness they settled down and
started to work right. Now I'm sure it could handle boost.
This carb has 26mm venturis and this seems to cause a significant lean spot at
around 2000 rpm that is so bad it basically wants to stop running unless you
catch it in time. I recall test running it last year and the lean spot would make the
whole car buck and wouldn't get better the more you got on it. The only thing
that worked is to let off, push in the clutch, and try again.
The guy who race prepped this carb obviously wasn't interested in having it run
well at low RPM. I'm kinda interested though. I'd like to use it in something as a
daily driver but this nasty lean spot just ruins the experience.
I think I'll consider swapping out the 26mm hogged venturis for some ranging
from 24.9mm up to 25.4mm. That seems to be about the biggest you can go and
not have too much of a lean spot.
Oh by the way the secondaries are hogged to 31mm and would show
13.something on the wideband when I'd floor it free reving (NA). Of course actual
driving will tell me for sure whether the air bleeds and/or jets should be
changed. The slow bleeds are solder filled. Sec fuel jets are 160 and sec main air
bleeds are 140.
loaded rods like your carb, which I've since abolished. I installed a set of new
needles and seats and needed to make sure the fuel level would be in the
middle of the windows. After some semi-floodiness they settled down and
started to work right. Now I'm sure it could handle boost.
This carb has 26mm venturis and this seems to cause a significant lean spot at
around 2000 rpm that is so bad it basically wants to stop running unless you
catch it in time. I recall test running it last year and the lean spot would make the
whole car buck and wouldn't get better the more you got on it. The only thing
that worked is to let off, push in the clutch, and try again.
The guy who race prepped this carb obviously wasn't interested in having it run
well at low RPM. I'm kinda interested though. I'd like to use it in something as a
daily driver but this nasty lean spot just ruins the experience.
I think I'll consider swapping out the 26mm hogged venturis for some ranging
from 24.9mm up to 25.4mm. That seems to be about the biggest you can go and
not have too much of a lean spot.
Oh by the way the secondaries are hogged to 31mm and would show
13.something on the wideband when I'd floor it free reving (NA). Of course actual
driving will tell me for sure whether the air bleeds and/or jets should be
changed. The slow bleeds are solder filled. Sec fuel jets are 160 and sec main air
bleeds are 140.
04-07-15, 01:02 AM
#90
3)118 primary fuel jets.
So far I think the carb needs 122s so I'll just drill them out next time I get a
chance.
4)90 air bleeds.
These are stock for 79 carbs and probably aren't the problem but they do make
the primary fuel jets seem small and insignificant. I'm still thinking with 70 air
bleeds on the brain because that's what most FB carbs come with. This is the
first SA carb I've ever tuned for boost so this is all kinda new for me.
So far I think the carb needs 122s so I'll just drill them out next time I get a
chance.
4)90 air bleeds.
These are stock for 79 carbs and probably aren't the problem but they do make
the primary fuel jets seem small and insignificant. I'm still thinking with 70 air
bleeds on the brain because that's what most FB carbs come with. This is the
first SA carb I've ever tuned for boost so this is all kinda new for me.
air bleeds to see if I could get a set of solder filled jets drilled to .72mm to fit.
I had to mod both the jets and air bleeds a lot to get them to fit together and
not be too tall. They do fit under the air horn probably well enough now to
work. The only problem is solder bloom which occurs over time in a moist (car)
environment. Crystals grow and will block the tiny .72mm holes eventually. So
this is only a temp tuning aid.
Then I realized I don't need to bother with 70 air bleeds in an SA carb so I
decided to tune for the 90 air bleeds. The first step is slightly larger primary fuel
jets ie the 122s I just drilled.
So that's #3 and #4 off the list. I have a feeling getting rid of the calibrated
boost leak #5 or making it a lot smaller will help reduce or stop the tendency to
go lean as RPMs rise. I think float level #1 will take care of itself or I'll reset it
later, and the brass tubes #2 might not require any attention. More time driving
it will let me know.
04-07-15, 06:10 AM
#91
carb whisperer
Congrats!
It's nice to see someone else having success with these carbs.
You followed my tuning advice. Could that be why it's tuned pretty well right
out of the box? Or are you pulling my leg?
Hmm, 14.0 at cruise sounds lean to me, but then I have a turbo and a ported
13B asking for a lot more air at the same RPM as you.
Nice idle AFR. Question: how much air and fuel screw threads do you have
available for tuning the idle? Like are both screws almost all the way in or are
they several turns out in a normal range?
What about the idle speed at 950? Does it not go any lower? Are you wanting it
to go lower? Does it vibrate? I don't understand.
Are the secondaries easier to open when the engine isn't running? Maybe the
way you tied them together is causing a bind? And yes vacuum does help hold
them closed to some extend. It's due to the way the blade is offset in the shaft.
Yep, typical mech secondary behavior. You gotta love it!
Ah, the 1500 to 2000 lean spot. Glad it's so small on your carb.
Don't go too small on the slow air bleeds.
Be my guest! Youll find after about six carbs that you want to stop. lol You'll go
stir craz- no you'll go Sterling Crazy! Kinda like he did.
It's nice to see someone else having success with these carbs.
You followed my tuning advice.
Could that be why it's tuned pretty well right out of the box? Or are you pulling my leg?
Hmm, 14.0 at cruise sounds lean to me, but then I have a turbo and a ported
13B asking for a lot more air at the same RPM as you.
Nice idle AFR. Question: how much air and fuel screw threads do you have
available for tuning the idle? Like are both screws almost all the way in or are
they several turns out in a normal range?
What about the idle speed at 950? Does it not go any lower? Are you wanting it
to go lower? Does it vibrate? I don't understand.
Are the secondaries easier to open when the engine isn't running? Maybe the
way you tied them together is causing a bind? And yes vacuum does help hold
them closed to some extend. It's due to the way the blade is offset in the shaft.
Yep, typical mech secondary behavior. You gotta love it!
Ah, the 1500 to 2000 lean spot. Glad it's so small on your carb.
Don't go too small on the slow air bleeds.
Be my guest! Youll find after about six carbs that you want to stop. lol You'll go
stir craz- no you'll go Sterling Crazy! Kinda like he did.
I want my idle to be slightly lower yes, but maybe only 50-100 rpm, so its close enough.
My air screw is turned all the way in, and my fuel mixture screw is in normal range.
The secondary blades only feel like they are sticking when its running. Never when it isnt lol.
04-07-15, 12:02 PM
#92
I guess I still don't understand about your idle. Can't you turn a screw and get it
down to 900? I can make mine idle at 400 if I wanted to. I like to keep it at
around 1000 because when the electric fan kicks on it drags the RPM down to
about 900 or so. I honestly don't pay much attention because the idle varies a
bit by temp anyway. All the modded Nikkis I've tested do this so I take it to mean
this is normal when you no longer have an altitude compensator (controlled
variable vacuum leak is is more like it) and the venturis are hogged out.
You say your air screw is all the way in and your idle is higher than you'd like.
Sounds like a small vacuum leak somewhere. I have to keep my air screw a
couple turns out*. My fuel screw is also only a couple turns out. This is due to the
100 short slow primary air bleeds I decided to try. If I went with 118s I could
back the fuel screw out a couple more turns into the normal range.
*I'm amazed how senstive the air screw is. A little turn can go from 12 to 13 on
the wideband. I'm used to carbs that don't have an air screw.
As for the secondaries being stiff, I take it you're used to vacuum secondary
carbs where the secondary opening point is not very easy to feel when you floor
it. Once you go mechanical, the spring normally keeping the secondaries closed
along with the vacuum sucking them closed is what you have to overcome to
open the secondaries. I've gotten totally used to it so I don't even think of them
as being stiff or sticking (unless they are sticking which happen sometimes when
they sit and the little bit of fuel on them turns to varnish which I took care of with
WD-40). They feel completely normal to me. It's actually a good feature to keep
you from entering the secondaries during lightly spirited driving. Then when you
need to use the secondaries, there is no question when and where in the
throttle position they are.
If you want to talk about stiff springs, I honestly don't like how stiff the main
throttle return spring is on FB carbs. I prefer old school carbs where the spring is
a little less heavy. I especially feel it in the REPU with an FB carb. The 1st gens
obviously have more leverage at the pedal.
But overall I think your carb turned out well. How soon do you plan on adding a
turbo?
down to 900? I can make mine idle at 400 if I wanted to. I like to keep it at
around 1000 because when the electric fan kicks on it drags the RPM down to
about 900 or so. I honestly don't pay much attention because the idle varies a
bit by temp anyway. All the modded Nikkis I've tested do this so I take it to mean
this is normal when you no longer have an altitude compensator (controlled
variable vacuum leak is is more like it) and the venturis are hogged out.
You say your air screw is all the way in and your idle is higher than you'd like.
Sounds like a small vacuum leak somewhere. I have to keep my air screw a
couple turns out*. My fuel screw is also only a couple turns out. This is due to the
100 short slow primary air bleeds I decided to try. If I went with 118s I could
back the fuel screw out a couple more turns into the normal range.
*I'm amazed how senstive the air screw is. A little turn can go from 12 to 13 on
the wideband. I'm used to carbs that don't have an air screw.
As for the secondaries being stiff, I take it you're used to vacuum secondary
carbs where the secondary opening point is not very easy to feel when you floor
it. Once you go mechanical, the spring normally keeping the secondaries closed
along with the vacuum sucking them closed is what you have to overcome to
open the secondaries. I've gotten totally used to it so I don't even think of them
as being stiff or sticking (unless they are sticking which happen sometimes when
they sit and the little bit of fuel on them turns to varnish which I took care of with
WD-40). They feel completely normal to me. It's actually a good feature to keep
you from entering the secondaries during lightly spirited driving. Then when you
need to use the secondaries, there is no question when and where in the
throttle position they are.
If you want to talk about stiff springs, I honestly don't like how stiff the main
throttle return spring is on FB carbs. I prefer old school carbs where the spring is
a little less heavy. I especially feel it in the REPU with an FB carb. The 1st gens
obviously have more leverage at the pedal.
But overall I think your carb turned out well. How soon do you plan on adding a
turbo?
04-07-15, 03:38 PM
#93
carb whisperer
Car is getting new paint+mariah hatch and 16x8 xxr 537's AND fender flares in a week.
After that I was looking at a turbo. All I know is I want it small. As close to the s4 t2 size as possible, since im limited to a t3/t4 flange for the manifold.
Also, if I remove my PCV valve the idle drops to around 900. It accounts for a tiny vac leak inline since its sucking the vapors from the crankcase. The crankcase has an open fresh air inlet going towards the charcoal canister.
After that I was looking at a turbo. All I know is I want it small. As close to the s4 t2 size as possible, since im limited to a t3/t4 flange for the manifold.
Also, if I remove my PCV valve the idle drops to around 900. It accounts for a tiny vac leak inline since its sucking the vapors from the crankcase. The crankcase has an open fresh air inlet going towards the charcoal canister.
04-07-15, 04:21 PM
#94
Ah, I understand now. That is why your air screw has to be all the way in and
your idle is higher than you'd like. Sometimes a small restrictor can be added if
the PCV valve acts like too much of a vacuum leak.
But once you go turbo, you can't use a traditional PCV valve. I haven't figure out
a viable way to get all the crankcase vapors out yet, but I did manage to get
most of them out with a hose running from the oil fill tube down to the filter
elbow in front of the turbo. The filter creates a tiny vacuum which sucks most of
the vapors. I still get moisture under the cap some days. Usually more when it's
cold out.
The nipple on the intermediate plate has a hose that is open to fresh air with no
filter.
Some people get a catch can but I haven't looked into them. Others drill a hole in
their oil fill cap which works great. No more moisture.
An actual S4 T2 turbo would be great. It's already a good size for a 12A. The
flange is kinda odd shaped but doable. As far as aftermarket small turbos, I don't
really know. Plus you have to install an external wastegate further complicating
the install.
Um I do have a small aftermarket cheap chinese turbo with a T4 exhaust housing (1.00 A/R) and
a small cold side. Its specs are:
Cold:
70.00mm
54.14mm
Hot:
73.45mm
63.15mm
I understand this turbo is capable of about 300HP on a 13B under 14psi. Not
sure what it would do at lower PSI as I'm a bit of a noob to turbos. I only know
what an S5 turbo can do because it's what I've used so far.
your idle is higher than you'd like. Sometimes a small restrictor can be added if
the PCV valve acts like too much of a vacuum leak.
But once you go turbo, you can't use a traditional PCV valve. I haven't figure out
a viable way to get all the crankcase vapors out yet, but I did manage to get
most of them out with a hose running from the oil fill tube down to the filter
elbow in front of the turbo. The filter creates a tiny vacuum which sucks most of
the vapors. I still get moisture under the cap some days. Usually more when it's
cold out.
The nipple on the intermediate plate has a hose that is open to fresh air with no
filter.
Some people get a catch can but I haven't looked into them. Others drill a hole in
their oil fill cap which works great. No more moisture.
An actual S4 T2 turbo would be great. It's already a good size for a 12A. The
flange is kinda odd shaped but doable. As far as aftermarket small turbos, I don't
really know. Plus you have to install an external wastegate further complicating
the install.
Um I do have a small aftermarket cheap chinese turbo with a T4 exhaust housing (1.00 A/R) and
a small cold side. Its specs are:
Cold:
70.00mm
54.14mm
Hot:
73.45mm
63.15mm
I understand this turbo is capable of about 300HP on a 13B under 14psi. Not
sure what it would do at lower PSI as I'm a bit of a noob to turbos. I only know
what an S5 turbo can do because it's what I've used so far.
04-08-15, 10:54 AM
#95
There may be a siphon effect; NA; solder filled slow bleeds, leads to flooding
Something I noticed free reving the racing nikki and another carb with the carb
hat off (NA mode, more or less). Fuel seemed to get siphoned out of the
secondary boosters which ran the bowls dry and fuel was pooling on the
secondary butterflies.
Why did the carb do this?
I think it's because the secondary slow bleeds are filled with solder so there is
no way to break the siphon effect until the RPMs drop low enough for long
enough or the engine stalls from being too rich and having empty float bowls at
the same time.
Weird, right?
Even more weird is the needles and seats are brand new so if anything the
bowls should be overfilled.
I inadvertantly shut it off when the engine was running pig-rich and sputtering,
before the bowls had a chance to refill, so I could check what was going on and
noticed the bowls were empty, not overly full.
It seems to do it after a few revs to redline when the secondaries close. Fuel
must be flowing hard out of the sec boosters but now it has no place to go and
just pools on the secondary butterflies, and continues until the bowls run dry.
Obviously this happens quickly at 2.5psi with the carb hat removed so the
mallory can't sense boost and raise fuel pressure to keep the bowls filled.
I think when the carb hat is installed this siphon effect doesn't occur as much
due to the incoming pressurized air. It breaks the siphon much sooner and
doesn't require the engine to run at a low RPM for a while or to stall before it
corrects itself. In other words it recovers fine when in "turbo mode".
So be cautious if you fill your secondary slow bleeds with solder and run it NA.
This weird flooding effect could happen to you while free reving or possibly while
driving hard. It's enough reason to put normal sec slows back in any carb that'll
be used NA and just rely on the accel pump mod to get past any secondary
hiccups. This has worked fine for me back when I was doing NA testing last year.
And that's even with my leaky brake booster! So you guys should be fine. Of
course your results may vary. Always gotta add that part.
hat off (NA mode, more or less). Fuel seemed to get siphoned out of the
secondary boosters which ran the bowls dry and fuel was pooling on the
secondary butterflies.
Why did the carb do this?
I think it's because the secondary slow bleeds are filled with solder so there is
no way to break the siphon effect until the RPMs drop low enough for long
enough or the engine stalls from being too rich and having empty float bowls at
the same time.
Weird, right?
Even more weird is the needles and seats are brand new so if anything the
bowls should be overfilled.
I inadvertantly shut it off when the engine was running pig-rich and sputtering,
before the bowls had a chance to refill, so I could check what was going on and
noticed the bowls were empty, not overly full.
It seems to do it after a few revs to redline when the secondaries close. Fuel
must be flowing hard out of the sec boosters but now it has no place to go and
just pools on the secondary butterflies, and continues until the bowls run dry.
Obviously this happens quickly at 2.5psi with the carb hat removed so the
mallory can't sense boost and raise fuel pressure to keep the bowls filled.
I think when the carb hat is installed this siphon effect doesn't occur as much
due to the incoming pressurized air. It breaks the siphon much sooner and
doesn't require the engine to run at a low RPM for a while or to stall before it
corrects itself. In other words it recovers fine when in "turbo mode".
So be cautious if you fill your secondary slow bleeds with solder and run it NA.
This weird flooding effect could happen to you while free reving or possibly while
driving hard. It's enough reason to put normal sec slows back in any carb that'll
be used NA and just rely on the accel pump mod to get past any secondary
hiccups. This has worked fine for me back when I was doing NA testing last year.
And that's even with my leaky brake booster! So you guys should be fine. Of
course your results may vary. Always gotta add that part.
Last edited by Jeff20B; 04-08-15 at 11:00 AM.
04-08-15, 07:30 PM
#96
carb whisperer
Fixed my idle issue, and I think I fixed the "sticking" feeling my secondaries had.
There was a physical *pop* sometimes at my pedal and it was worrying me that they were binding, so I pulled the carb off to inspect the linkages off the car. They were free moving, but indeed binding if they returned to closed quickly. So, I did the old thumb on the leading edge trick until they couldnt stick anymore and goosed down the screws.
While I was in there, I pulled the throttle body off and found my custom thick gasket had a tear leading from one of the corners of the carb to the rotor 1 primary float. How did this happen?
I made a new one, and then painted it with Shellac "Indian Head" for good measure. I waited for it to tack up, and carefully put everything together. I torqued all the bolts and got a good seal around the throttles.
When I started it up, and BAM it wouldnt idle above 200 RPM. I adjusted it all up and brought the air screw back in to normal range and carefully brought the bump stop up for proper linkage pull action.
Now it happily idles closer to 12.0:1 instead of 12.5:1 but whatever.
The idle is dead smooth at 900 RPM and I can make it idle all the way down to 500 RPM.
There was a physical *pop* sometimes at my pedal and it was worrying me that they were binding, so I pulled the carb off to inspect the linkages off the car. They were free moving, but indeed binding if they returned to closed quickly. So, I did the old thumb on the leading edge trick until they couldnt stick anymore and goosed down the screws.
While I was in there, I pulled the throttle body off and found my custom thick gasket had a tear leading from one of the corners of the carb to the rotor 1 primary float. How did this happen?
I made a new one, and then painted it with Shellac "Indian Head" for good measure. I waited for it to tack up, and carefully put everything together. I torqued all the bolts and got a good seal around the throttles.
When I started it up, and BAM it wouldnt idle above 200 RPM. I adjusted it all up and brought the air screw back in to normal range and carefully brought the bump stop up for proper linkage pull action.
Now it happily idles closer to 12.0:1 instead of 12.5:1 but whatever.
The idle is dead smooth at 900 RPM and I can make it idle all the way down to 500 RPM.
04-08-15, 07:33 PM
#97
carb whisperer
Filled some of my shitty 160 slow air bleeds with epoxy, and drilled them to 1mm.
Filled some of my shitty 140 secondary main air bleeds with epoxy and drilled them to 1mm.
Installed Mazdatrix 125 primary mains.
Perfect tune
Cruises at 13.5:1, power comes on with no bog at all from the secondaries at 12.8:1-12.5:1 all the way from 3k RPM to 8k RPM.
Idles perfectly at 12.0:1
No primary bog at 1500-2000 rpm.
Now all I need to address is my leaking accel pump gaskets...
Filled some of my shitty 140 secondary main air bleeds with epoxy and drilled them to 1mm.
Installed Mazdatrix 125 primary mains.
Perfect tune
Cruises at 13.5:1, power comes on with no bog at all from the secondaries at 12.8:1-12.5:1 all the way from 3k RPM to 8k RPM.
Idles perfectly at 12.0:1
No primary bog at 1500-2000 rpm.
Now all I need to address is my leaking accel pump gaskets...
04-08-15, 11:34 PM
#98
Yes, sometimes I'd get the *pop* from my secondaries. The Racing Nikki would
do it more often than the others. Then it mysteriously disappeared and never did
it again. Then the other carbs had the stiff secondaries, which stopped after WD-
40 and never came back, even though there's been gas on them. I guess they
broke in.
Wow, you got your carb tuned amazingly well! I'm kinda jealous because my
carbs aren't as stable as that. Of course I'm not spending 100% tuning time on
any one carb. Plus I'm asking more from them than they were designed for. I
also cut my venturis by hand, which I'm sure makes them less efficient than
yours. I gotta grab the 25.4mm ones and redo them slightly in the middle, for
example, due to a less than perfect shape. Of course this carb doesn't have the
lean spot between 1500 to 2000 either, but it does have a soggy bottom end.
Could be related.
Speaking of which, I'm retiring the Racing Nikki as a daily driver carb because the
venturis are 26mm and have too much of a nasty flat spot at and above 2000 for
my liking. I honestly don't want to tear into it and take out the 26mm venturis to
replace with a smaller set, which I'd have to cut. By hand. To 25mm or so. Plus
the guy who built it probably used red loctite on them or something. It is a racing
carb after all. I'd rather leave it together to go on a streetported 12A I've got
sitting on a shelf for autocross use. Of course this 12A could drive a turbo at
least as well as a 74 ported 13B. It also has R5 side plates. Hmm... maybe.
The only engine I wanted to use the Racing Nikki on was a mild streetported 13B
in the rotary MG, but not with it acting this badly. So I spent part of the day
bench tuning three carbs for NA use.
1. I decided to retune the 25.15mm carb for NA in the MG because it
doesn't like boost for some reason - floods itself out as if it's experiencing the
secondary siphon effect described above, but it's the only boost prepped carb
out of all four FB carbs that does this. I thought maybe the needles and seats
simply needed more break in time but now I know that's just a bunch of hooey.
Two other carbs have proven that they only need to seat well enough to keep
the fuel levels in the middles of the windows at idle at which point they'll handle
boost just fine. This carb got a set of Holley 51s as fuel jets (about 1.29mm) so
we'll see how rich this thing runs on primaries. Secondaries are all stock.
It should be a great carb for the MG if the previous stock 74 Hitachi with clogged
secondaries is any indication. Going from 22mm to 25.15mm on primaries alone
should put some spark back in my plugs. Then mechanical secondaries will
require Dr Budmonger to help enclench me.
2. The 79-80 hybrid carb was tuned for boost the other day, mentioned
above, and tested but it leaned out (17 on the wideband) at the top of primaries
only to go back to 10.0 when the secondaries opened with no secondary delay.
So some in-depth boost tuning is needed, but for now should do ok with an NA
tune. I'd like this carb to go in the GLC as it only has a 74 ported 13B and will
get an NO manifold.
3. The Racing Nikki was put back to racing specs. It got some RX-3 floats
and Grose jets. The fuel jets were chosen as a mathmatical middle road between
the 155s it had when I got it and the 137s I tested in it recently. 155-137=18.
Half of 18 is 9. So 9+137=146. I just happen to have a 1.46mm drill bit. If the
146s turn out to be too rich, I can swap in some 141s or the 137s again. And the
secondaries are 185s. Air bleeds are standard SA 90 and 140.
I was going to NA tune a fourth carb but ran out of secondary long slow bleeds.
This carb was going in the REPU but looks like I can't do that as soon as I
wanted. So as the carb sits it is currently tuned for a turbo. Maybe it would work
ok for NA, but after the weird secondary siphon issue, I'd rather forgo the
hogged Nikki and throw the Camden back in because I did like how it drove
here. Plus I don't have everything ready to go turbo just yet. Still need several
parts. I think while I gather everything, the SC can make itself useful.
Getting back to your posts, I like that you filled your 160s and 140s with epoxy
and drilled them already. 1mm is a good starting point. Ever since I discovered
why mine was having such a long secondary delay with boost, I'm now going to
begin enlarging my sec main air bleeds little by little until I get back to 11 AFR.
They're currently at 91. Who knows, maybe 118 will be my magic number again?
But I've got 92, 94, 100 and 106 to try first, plus I can do any oddball sizes with
the micro drillbits if they're available like 98 and maybe 109 or something. I know
I have 105 because I used it recently.
You have leaking accel pump gaskets? My first set got moist and attracted dirt
but never actually leaked, back in 2006 or whenever I did them. Seen in the Nikki
and Mani thread. That's now the 25.15mm carb, by the way. A little history.
Did you watch for the accel pump casting to flex and compress at the four screw
holes? I noticed SA and older ones do that. Could be the real reason for the leak.
The gray paper I use only gets slightly dark when gas soaks into it but I have
not seen any actual leaks from it other than if the housing is warped. That
includes the main body against the cast iron throttle body or baseplate, such as
the Racing Nikki making it a lousy candidate for boost,a nd it happens to be an
SA carb.
do it more often than the others. Then it mysteriously disappeared and never did
it again. Then the other carbs had the stiff secondaries, which stopped after WD-
40 and never came back, even though there's been gas on them. I guess they
broke in.
Wow, you got your carb tuned amazingly well! I'm kinda jealous because my
carbs aren't as stable as that. Of course I'm not spending 100% tuning time on
any one carb. Plus I'm asking more from them than they were designed for. I
also cut my venturis by hand, which I'm sure makes them less efficient than
yours. I gotta grab the 25.4mm ones and redo them slightly in the middle, for
example, due to a less than perfect shape. Of course this carb doesn't have the
lean spot between 1500 to 2000 either,
but it does have a soggy bottom end. Could be related.
Speaking of which, I'm retiring the Racing Nikki as a daily driver carb because the
venturis are 26mm and have too much of a nasty flat spot at and above 2000 for
my liking. I honestly don't want to tear into it and take out the 26mm venturis to
replace with a smaller set, which I'd have to cut. By hand. To 25mm or so. Plus
the guy who built it probably used red loctite on them or something. It is a racing
carb after all. I'd rather leave it together to go on a streetported 12A I've got
sitting on a shelf for autocross use. Of course this 12A could drive a turbo at
least as well as a 74 ported 13B. It also has R5 side plates. Hmm... maybe.
The only engine I wanted to use the Racing Nikki on was a mild streetported 13B
in the rotary MG, but not with it acting this badly. So I spent part of the day
bench tuning three carbs for NA use.
1. I decided to retune the 25.15mm carb for NA in the MG because it
doesn't like boost for some reason - floods itself out as if it's experiencing the
secondary siphon effect described above, but it's the only boost prepped carb
out of all four FB carbs that does this. I thought maybe the needles and seats
simply needed more break in time but now I know that's just a bunch of hooey.
Two other carbs have proven that they only need to seat well enough to keep
the fuel levels in the middles of the windows at idle at which point they'll handle
boost just fine. This carb got a set of Holley 51s as fuel jets (about 1.29mm) so
we'll see how rich this thing runs on primaries. Secondaries are all stock.
It should be a great carb for the MG if the previous stock 74 Hitachi with clogged
secondaries is any indication. Going from 22mm to 25.15mm on primaries alone
should put some spark back in my plugs. Then mechanical secondaries will
require Dr Budmonger to help enclench me.
2. The 79-80 hybrid carb was tuned for boost the other day, mentioned
above, and tested but it leaned out (17 on the wideband) at the top of primaries
only to go back to 10.0 when the secondaries opened with no secondary delay.
So some in-depth boost tuning is needed, but for now should do ok with an NA
tune. I'd like this carb to go in the GLC as it only has a 74 ported 13B and will
get an NO manifold.
3. The Racing Nikki was put back to racing specs. It got some RX-3 floats
and Grose jets. The fuel jets were chosen as a mathmatical middle road between
the 155s it had when I got it and the 137s I tested in it recently. 155-137=18.
Half of 18 is 9. So 9+137=146. I just happen to have a 1.46mm drill bit. If the
146s turn out to be too rich, I can swap in some 141s or the 137s again. And the
secondaries are 185s. Air bleeds are standard SA 90 and 140.
I was going to NA tune a fourth carb but ran out of secondary long slow bleeds.
This carb was going in the REPU but looks like I can't do that as soon as I
wanted. So as the carb sits it is currently tuned for a turbo. Maybe it would work
ok for NA, but after the weird secondary siphon issue, I'd rather forgo the
hogged Nikki and throw the Camden back in because I did like how it drove
here. Plus I don't have everything ready to go turbo just yet. Still need several
parts. I think while I gather everything, the SC can make itself useful.
Getting back to your posts, I like that you filled your 160s and 140s with epoxy
and drilled them already. 1mm is a good starting point. Ever since I discovered
why mine was having such a long secondary delay with boost, I'm now going to
begin enlarging my sec main air bleeds little by little until I get back to 11 AFR.
They're currently at 91. Who knows, maybe 118 will be my magic number again?
But I've got 92, 94, 100 and 106 to try first, plus I can do any oddball sizes with
the micro drillbits if they're available like 98 and maybe 109 or something. I know
I have 105 because I used it recently.
You have leaking accel pump gaskets? My first set got moist and attracted dirt
but never actually leaked, back in 2006 or whenever I did them. Seen in the Nikki
and Mani thread. That's now the 25.15mm carb, by the way.
A little history.Did you watch for the accel pump casting to flex and compress at the four screw
holes? I noticed SA and older ones do that. Could be the real reason for the leak.
The gray paper I use only gets slightly dark when gas soaks into it but I have
not seen any actual leaks from it other than if the housing is warped. That
includes the main body against the cast iron throttle body or baseplate, such as
the Racing Nikki making it a lousy candidate for boost,a nd it happens to be an
SA carb.
Last edited by Jeff20B; 04-09-15 at 12:18 AM.
04-09-15, 08:14 AM
#99
carb whisperer
You have leaking accel pump gaskets? My first set got moist and attracted dirt
but never actually leaked, back in 2006 or whenever I did them. Seen in the Nikki
and Mani thread. That's now the 25.15mm carb, by the way. A little history.
Did you watch for the accel pump casting to flex and compress at the four screw
holes? I noticed SA and older ones do that. Could be the real reason for the leak.
The gray paper I use only gets slightly dark when gas soaks into it but I have
not seen any actual leaks from it other than if the housing is warped. That
includes the main body against the cast iron throttle body or baseplate, such as
the Racing Nikki making it a lousy candidate for boost,a nd it happens to be an
SA carb.
but never actually leaked, back in 2006 or whenever I did them. Seen in the Nikki
and Mani thread. That's now the 25.15mm carb, by the way.
A little history.Did you watch for the accel pump casting to flex and compress at the four screw
holes? I noticed SA and older ones do that. Could be the real reason for the leak.
The gray paper I use only gets slightly dark when gas soaks into it but I have
not seen any actual leaks from it other than if the housing is warped. That
includes the main body against the cast iron throttle body or baseplate, such as
the Racing Nikki making it a lousy candidate for boost,a nd it happens to be an
SA carb.
