Thinking about ditching the IDA
10-19-15, 10:46 PM
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Thinking about ditching the IDA
Hey everyone, I have a Weber 48 Ida carb on my 83 GSL right now, but I'm getting about 10mpg, and I can't really afford to drive the car which defeats the purpose of having it. So, if you don't mind I have a few questions for you more experiences rotary guys.
-I hear a lot of talk about the stock carb being a Nikki, what exactly is the model of the carb?
-will the stock carb fit on the intake for the Ida?
-is the stock carb a 4 or 2 barrel? (I searched, but it just got me more confused, a straight answer would be greatly appreciated!)
-what kind of fuel economy could I expect out of the stock carb?
And lastly, would there be any interest if I were to post a trade thread for an original carb?
Thanks everyone!
-Rotospectre
-I hear a lot of talk about the stock carb being a Nikki, what exactly is the model of the carb?
-will the stock carb fit on the intake for the Ida?
-is the stock carb a 4 or 2 barrel? (I searched, but it just got me more confused, a straight answer would be greatly appreciated!)
-what kind of fuel economy could I expect out of the stock carb?
And lastly, would there be any interest if I were to post a trade thread for an original carb?
Thanks everyone!
-Rotospectre
10-19-15, 10:57 PM
#2
Hey everyone, I have a Weber 48 Ida carb on my 83 GSL right now, but I'm getting about 10mpg, and I can't really afford to drive the car which defeats the purpose of having it. So, if you don't mind I have a few questions for you more experiences rotary guys. -I hear a lot of talk about the stock carb being a Nikki, what exactly is the model of the carb? -will the stock carb fit on the intake for the Ida? -is the stock carb a 4 or 2 barrel? (I searched, but it just got me more confused, a straight answer would be greatly appreciated!) -what kind of fuel economy could I expect out of the stock carb? And lastly, would there be any interest if I were to post a trade thread for an original carb? Thanks everyone! -Rotospectre
10-20-15, 12:05 AM
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Is the IDA and manifold really that big of an improvement over the factory setup? I don't mean to ask dumb questions, but I've always been a domestic guy, and it just seems like a 4bbl would be the obvious choice for power over a 2bbl, unless the 2bbl flows that much more. I'm looking for a little bit more gas mileage, but I don't want to sacrifice too much power.
And thanks for the offer, I'm going to check out my local used parts yard, but I may message you sometime if you want to sell anything.
And thanks for the offer, I'm going to check out my local used parts yard, but I may message you sometime if you want to sell anything.
10-20-15, 12:48 AM
#7
First I'll say you are right that the IDA is an improvement over the FACTORY setup. However a modified Nikki on a freer flowing intake manifold will be right up there with the IDA. And then if you set up the Nikki to be hogged out and boost prepped, it will tower over the IDA in power and get better gas mileage to boot! That is why I have no need for an IDA. They just don't do it for me.
If you think about it, the rotary has a wide rev range. The problem with a 2bbl carb was that it was designed to work on a lazy 4cyl where each cylinder gets its own barrel. To make a 2bbl work on a rotary, you have to get the biggest idle jet they make, which is a 100, and drill it out to 120. Then you have to let the carb "idle" on the 1st transition hole. That ain't right. lol Then you have to find an F tube that will work because no one ever mass produced them for a rotary. And then you still don't have secondaries! What you're left with is a carb that might run well from idle up to about mid RPM, or a carb that does well from mid RPM up to redline, but it doesn't cover the entire rev range as nicely as a 4bbl. It always leaves you wanting - in your case wanting better gas mileage. And then if you are thinking about throwing boost at it, good luck. It's either too rich at low RPM but just right at high RPM, or ok at low RPM but too lean at high RPM in boost. That equals kaboom.
The only good reason to run a 2bbl on a rotary is if you have a peripheral port. The limitations of the carb are outweighed by the freer breathing capabilities of the port. But then EFI tends to get past all the problems that a p-port has, with its massive overlap and limited vacuum signal at low RPM, thus rendering 2bbls on a rotary moot. But then some have had success with a carbed p-port like j9fd3s. But it took him a long time to get there. He had to throw out the commonly used jetting sheet and just start over from scratch. Give the engine what it wants and ignore everything (and everybody) else.
That's what I had to do on my hogged out boost prepped Nikkis to get them to work properly with boost. I took a device that was designed to work with vacuum, and gave it what it wanted in order to handle boost. Turned out really well. Better than any 2bbl and even gives EFI a run for its money.
But getting back to your topic, you would need a hogged out modified Nikki, some sort of free flowing intake manifold, and a stock phenolic spacer. Also a brake booster fitting and a PCV valve or equivalent. You would also need a free flowing air filter. The only problem is if I provided these parts, I wouldn't have them anymore. Kind of a bummer.
If I did get your IDA, I'd probably turn around and list it up on the forum as soon as possible. I'm sure it would sell because they always do.
Something else to think about. The reason the Nikki runs so well on the rotary is because it was designed for a rotary in the first place.
But they are a very small carb meant for gas mileage and not so much for power. That is where modding them comes in; to make them a much bigger carb. However you can't just buy parts off the shelf like you can with a weber. Most folks like webers because there are a lot of parts out there, and I understand that. Modding a Nikki requires a different skill set and a different mentality; one of self sufficiency because there are no off the shelf parts. Actually, there is a source of Hitachi jets that fit, so we do have some support. 
If you think about it, the rotary has a wide rev range. The problem with a 2bbl carb was that it was designed to work on a lazy 4cyl where each cylinder gets its own barrel. To make a 2bbl work on a rotary, you have to get the biggest idle jet they make, which is a 100, and drill it out to 120. Then you have to let the carb "idle" on the 1st transition hole. That ain't right. lol Then you have to find an F tube that will work because no one ever mass produced them for a rotary. And then you still don't have secondaries! What you're left with is a carb that might run well from idle up to about mid RPM, or a carb that does well from mid RPM up to redline, but it doesn't cover the entire rev range as nicely as a 4bbl. It always leaves you wanting - in your case wanting better gas mileage. And then if you are thinking about throwing boost at it, good luck. It's either too rich at low RPM but just right at high RPM, or ok at low RPM but too lean at high RPM in boost. That equals kaboom.
The only good reason to run a 2bbl on a rotary is if you have a peripheral port. The limitations of the carb are outweighed by the freer breathing capabilities of the port. But then EFI tends to get past all the problems that a p-port has, with its massive overlap and limited vacuum signal at low RPM, thus rendering 2bbls on a rotary moot. But then some have had success with a carbed p-port like j9fd3s. But it took him a long time to get there. He had to throw out the commonly used jetting sheet and just start over from scratch. Give the engine what it wants and ignore everything (and everybody) else.
That's what I had to do on my hogged out boost prepped Nikkis to get them to work properly with boost. I took a device that was designed to work with vacuum, and gave it what it wanted in order to handle boost. Turned out really well. Better than any 2bbl and even gives EFI a run for its money.
But getting back to your topic, you would need a hogged out modified Nikki, some sort of free flowing intake manifold, and a stock phenolic spacer. Also a brake booster fitting and a PCV valve or equivalent. You would also need a free flowing air filter. The only problem is if I provided these parts, I wouldn't have them anymore. Kind of a bummer.
If I did get your IDA, I'd probably turn around and list it up on the forum as soon as possible. I'm sure it would sell because they always do.
Something else to think about. The reason the Nikki runs so well on the rotary is because it was designed for a rotary in the first place.
But they are a very small carb meant for gas mileage and not so much for power. That is where modding them comes in; to make them a much bigger carb. However you can't just buy parts off the shelf like you can with a weber. Most folks like webers because there are a lot of parts out there, and I understand that. Modding a Nikki requires a different skill set and a different mentality; one of self sufficiency because there are no off the shelf parts. Actually, there is a source of Hitachi jets that fit, so we do have some support.
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10-20-15, 06:00 AM
#8
carb whisperer
First I'll say you are right that the IDA is an improvement over the FACTORY setup. However a modified Nikki on a freer flowing intake manifold will be right up there with the IDA. And then if you set up the Nikki to be hogged out and boost prepped, it will tower over the IDA in power and get better gas mileage to boot! That is why I have no need for an IDA. They just don't do it for me.
If you think about it, the rotary has a wide rev range. The problem with a 2bbl carb was that it was designed to work on a lazy 4cyl where each cylinder gets its own barrel. To make a 2bbl work on a rotary, you have to get the biggest idle jet they make, which is a 100, and drill it out to 120. Then you have to let the carb "idle" on the 1st transition hole. That ain't right. lol Then you have to find an F tube that will work because no one ever mass produced them for a rotary. And then you still don't have secondaries! What you're left with is a carb that might run well from idle up to about mid RPM, or a carb that does well from mid RPM up to redline, but it doesn't cover the entire rev range as nicely as a 4bbl. It always leaves you wanting - in your case wanting better gas mileage. And then if you are thinking about throwing boost at it, good luck. It's either too rich at low RPM but just right at high RPM, or ok at low RPM but too lean at high RPM in boost. That equals kaboom.
The only good reason to run a 2bbl on a rotary is if you have a peripheral port. The limitations of the carb are outweighed by the freer breathing capabilities of the port. But then EFI tends to get past all the problems that a p-port has, with its massive overlap and limited vacuum signal at low RPM, thus rendering 2bbls on a rotary moot. But then some have had success with a carbed p-port like j9fd3s. But it took him a long time to get there. He had to throw out the commonly used jetting sheet and just start over from scratch. Give the engine what it wants and ignore everything (and everybody) else.
That's what I had to do on my hogged out boost prepped Nikkis to get them to work properly with boost. I took a device that was designed to work with vacuum, and gave it what it wanted in order to handle boost. Turned out really well. Better than any 2bbl and even gives EFI a run for its money.
But getting back to your topic, you would need a hogged out modified Nikki, some sort of free flowing intake manifold, and a stock phenolic spacer. Also a brake booster fitting and a PCV valve or equivalent. You would also need a free flowing air filter. The only problem is if I provided these parts, I wouldn't have them anymore. Kind of a bummer.
If I did get your IDA, I'd probably turn around and list it up on the forum as soon as possible. I'm sure it would sell because they always do.
Something else to think about. The reason the Nikki runs so well on the rotary is because it was designed for a rotary in the first place. But they are a very small carb meant for gas mileage and not so much for power. That is where modding them comes in; to make them a much bigger carb. However you can't just buy parts off the shelf like you can with a weber. Most folks like webers because there are a lot of parts out there, and I understand that. Modding a Nikki requires a different skill set and a different mentality; one of self sufficiency because there are no off the shelf parts. Actually, there is a source of Hitachi jets that fit, so we do have some support.
If you think about it, the rotary has a wide rev range. The problem with a 2bbl carb was that it was designed to work on a lazy 4cyl where each cylinder gets its own barrel. To make a 2bbl work on a rotary, you have to get the biggest idle jet they make, which is a 100, and drill it out to 120. Then you have to let the carb "idle" on the 1st transition hole. That ain't right. lol Then you have to find an F tube that will work because no one ever mass produced them for a rotary. And then you still don't have secondaries! What you're left with is a carb that might run well from idle up to about mid RPM, or a carb that does well from mid RPM up to redline, but it doesn't cover the entire rev range as nicely as a 4bbl. It always leaves you wanting - in your case wanting better gas mileage. And then if you are thinking about throwing boost at it, good luck. It's either too rich at low RPM but just right at high RPM, or ok at low RPM but too lean at high RPM in boost. That equals kaboom.
The only good reason to run a 2bbl on a rotary is if you have a peripheral port. The limitations of the carb are outweighed by the freer breathing capabilities of the port. But then EFI tends to get past all the problems that a p-port has, with its massive overlap and limited vacuum signal at low RPM, thus rendering 2bbls on a rotary moot. But then some have had success with a carbed p-port like j9fd3s. But it took him a long time to get there. He had to throw out the commonly used jetting sheet and just start over from scratch. Give the engine what it wants and ignore everything (and everybody) else.
That's what I had to do on my hogged out boost prepped Nikkis to get them to work properly with boost. I took a device that was designed to work with vacuum, and gave it what it wanted in order to handle boost. Turned out really well. Better than any 2bbl and even gives EFI a run for its money.
But getting back to your topic, you would need a hogged out modified Nikki, some sort of free flowing intake manifold, and a stock phenolic spacer. Also a brake booster fitting and a PCV valve or equivalent. You would also need a free flowing air filter. The only problem is if I provided these parts, I wouldn't have them anymore. Kind of a bummer.
If I did get your IDA, I'd probably turn around and list it up on the forum as soon as possible. I'm sure it would sell because they always do.
Something else to think about. The reason the Nikki runs so well on the rotary is because it was designed for a rotary in the first place.
But they are a very small carb meant for gas mileage and not so much for power. That is where modding them comes in; to make them a much bigger carb. However you can't just buy parts off the shelf like you can with a weber. Most folks like webers because there are a lot of parts out there, and I understand that. Modding a Nikki requires a different skill set and a different mentality; one of self sufficiency because there are no off the shelf parts. Actually, there is a source of Hitachi jets that fit, so we do have some support. Now that work is slowing down im going to build a couple for sale over the winter.
10-20-15, 09:11 AM
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nah, rotary runs on a 55-65 idle jet, not much different than a piston engine, they do tend to run on the 1st transition hole though, as the rotary flows more air than a lazy piston engine. there are F tubes for the 13B and 12A, but nobody reads the chart and just uses the F11 which is for like a 1300cc VW engine or something.
10-20-15, 09:14 AM
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10-20-15, 09:17 AM
#12
To get back to the poster's original question, yes the stock Nikki will give you much better gas mileage, around 22-23 mpg is what is typically reported and that has always been my accurately measured number. If you're goal isn't to be faster than the next guy, the stock Nikki is a very nice match for the stock 12A. And if you want to regress towards IDA gas guzzling performance, you can hog it out (see Jeff, Tim and others posts on this for instructions).
The 4 barrel is better because most of the time it runs on the smaller primaries, making it very fuel efficient. Then when you do want an extra kick, the larger secondaries kick in, but only long enough to give that boost, then they stop sucking gas.
The good news is you can pick up a decent used Nikki for less than $100, if you can't find one locally they are on ebay all the time. And then you can sell your IDA for hundreds and hundreds of dollars, folks in the Weber Cults pay ridiculous sums for those silly little carbs.
You will need to go back to the stock intake manifold, but these aren't too hard to find. If you can't find one send me a pm with your mailing address and I'll get one in the mail for you, I have several extras.
And yes stock, hogged or boost prepped, Nikki's rule.
The 4 barrel is better because most of the time it runs on the smaller primaries, making it very fuel efficient. Then when you do want an extra kick, the larger secondaries kick in, but only long enough to give that boost, then they stop sucking gas.
The good news is you can pick up a decent used Nikki for less than $100, if you can't find one locally they are on ebay all the time. And then you can sell your IDA for hundreds and hundreds of dollars, folks in the Weber Cults pay ridiculous sums for those silly little carbs.
You will need to go back to the stock intake manifold, but these aren't too hard to find. If you can't find one send me a pm with your mailing address and I'll get one in the mail for you, I have several extras.
And yes stock, hogged or boost prepped, Nikki's rule.
10-20-15, 09:31 AM
#13
Originally Posted by j9fd3s
nah, rotary runs on a 55-65 idle jet, not much different than a piston engine, they do tend to run on the 1st transition hole though, as the rotary flows more air than a lazy piston engine. there are F tubes for the 13B and 12A, but nobody reads the chart and just uses the F11 which is for like a 1300cc VW engine or something.
Some weber cult member must have had some free time on his hands to try some test drills in some F tube blanks until he arrived at what worked best for his 13B and what worked best for his 12A. Right?
10-20-15, 12:43 PM
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Thanks for all the help guys! I'd be a happy camper if I could get around 20 mpg. The car I quick enough for me, I just love that it handles like it's on rails. Ray, I appreciate that, ill let you know if I need one, thanks!
I'm slightly confused though, you say that the seccondaries will open, then stop sucking, if they're vacume, shouldn't they stay open until you drop vacume, by closing the throttle or shifting, ECT?
There are a couple of 79-85 7's sitting in this used car parts place down the road from my house, ill be seeing If I can slavage anything off of them. I have big plans for this car! Its my second daily besides my S-10. I appreciate all the good info guys!
I'm slightly confused though, you say that the seccondaries will open, then stop sucking, if they're vacume, shouldn't they stay open until you drop vacume, by closing the throttle or shifting, ECT?
There are a couple of 79-85 7's sitting in this used car parts place down the road from my house, ill be seeing If I can slavage anything off of them. I have big plans for this car! Its my second daily besides my S-10. I appreciate all the good info guys!
10-20-15, 01:29 PM
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10-20-15, 01:33 PM
#16
Waffles - hmmm good
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So the best stock intake manifold is from a 1979/80 SA. Doesn't have the goofy coasting flapper
in it and flows better. I would go with a FB nikki, like say an 83 or so. Seems to have reasonable
jetting stock and is easy to modify as well.
Both Jeff and I have hogged our nikkis out and love em. Stock the secondaries are vacuum
operated but you can also set it up to have mechanical secondaries as well. I like the mech
secondaries, gives you a lot of control over when the gas flows heavy. I get 24mpg on the
highway and about 20mpg in town or in the mountains.
If you want to boost prep the nikki go read some of Jeff20bs threads on that topic. Wealth of
knowledge there.
in it and flows better. I would go with a FB nikki, like say an 83 or so. Seems to have reasonable
jetting stock and is easy to modify as well.
Both Jeff and I have hogged our nikkis out and love em. Stock the secondaries are vacuum
operated but you can also set it up to have mechanical secondaries as well. I like the mech
secondaries, gives you a lot of control over when the gas flows heavy. I get 24mpg on the
highway and about 20mpg in town or in the mountains.
If you want to boost prep the nikki go read some of Jeff20bs threads on that topic. Wealth of
knowledge there.
10-20-15, 01:43 PM
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Oh that's right. I seem to recall there were F tubes for 12A and 13B, which were a little different from each other. I vaguely remember thinking it odd they would be different, seeing as the engines are so similar (I'm getting a 12A carb to work great on a 13B), but then I figured it's just weber and weird.
Some weber cult member must have had some free time on his hands to try some test drills in some F tube blanks until he arrived at what worked best for his 13B and what worked best for his 12A. Right?
Some weber cult member must have had some free time on his hands to try some test drills in some F tube blanks until he arrived at what worked best for his 13B and what worked best for his 12A. Right?
some examples, the F11 on a rotary people tend to have an incurable flat spot around ~3000rpm, where the idle circuit is stopping working, and the mains aren't up to speed yet, so its a lean spot. my 12A with the F7, can go from a lean stumble, to so rich at that spot it stops running, so i was able to make that transition seamless. additionally it goes from ~14:1 at idle/part throttle, and gradually richens up to be in the 11's @wot and redline.
10-20-15, 05:15 PM
#18
"I'm slightly confused though, you say that the seccondaries will open, then stop sucking, if they're vacume, shouldn't they stay open until you drop vacume, by closing the throttle or shifting, ECT?"
You ADD guys, who actually know how these things work but have forgotten what the post was asking about, should correct me if I'm wrong.
As I understand it, the secondaries, which are vacuum operated, open up when you punch the gas and the engine revs up, creating more vacuum. With the secondaries open you're getting lots of power, along with about 3 mpg to make that power.
The secondaries stay open as long as you're revving the engine, asking for more power and maintaining a strong vacuum. Then when you let off the gas, the revs drop, vacuum decreases, secondaries close and you're back to 24-25 mpg.
That's why 4 barrels get better gas mileage than 2 barrels, most of the time they are operating on the smaller primaries, which use fuel more efficiently.
Now Tim, back when he had his two barrel Del Horto carb in his SA, used to claim that he was getting 28 mpg all day long with that hog. But I never believed him, and I would note that he's now ditched the two barrel Dels for a 4 barrel Nikki, hogged as it may be.
Concerning the relative merits of SA manifolds vs FB manifolds, now I know why Tim wanted me to check to see if I had any SA units in the shed!
I still need to check, but I think mine are all FB's.
But if the only difference between the FB and SA manifolds is that flappy thing that's connected to the shutter valve, that's no big deal. It can be removed and the pivot holes filled with JB weld.
If there are other advantages to the SA intake and I happen to have one in the shed, I guess Tim gets dibs and I need to start shopping.
You ADD guys, who actually know how these things work but have forgotten what the post was asking about, should correct me if I'm wrong.
As I understand it, the secondaries, which are vacuum operated, open up when you punch the gas and the engine revs up, creating more vacuum. With the secondaries open you're getting lots of power, along with about 3 mpg to make that power.
The secondaries stay open as long as you're revving the engine, asking for more power and maintaining a strong vacuum. Then when you let off the gas, the revs drop, vacuum decreases, secondaries close and you're back to 24-25 mpg.
That's why 4 barrels get better gas mileage than 2 barrels, most of the time they are operating on the smaller primaries, which use fuel more efficiently.
Now Tim, back when he had his two barrel Del Horto carb in his SA, used to claim that he was getting 28 mpg all day long with that hog. But I never believed him, and I would note that he's now ditched the two barrel Dels for a 4 barrel Nikki, hogged as it may be.
Concerning the relative merits of SA manifolds vs FB manifolds, now I know why Tim wanted me to check to see if I had any SA units in the shed!
I still need to check, but I think mine are all FB's.
But if the only difference between the FB and SA manifolds is that flappy thing that's connected to the shutter valve, that's no big deal. It can be removed and the pivot holes filled with JB weld.
If there are other advantages to the SA intake and I happen to have one in the shed, I guess Tim gets dibs and I need to start shopping.
Last edited by ray green; 10-20-15 at 05:21 PM.
10-21-15, 10:04 AM
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Anyone care to elaborate? 
So in case anyone is curious, I think I've formulated my plan.
My local used car parts lot, (like pull-a-part) has a 7 (Not sure what year) sitting with an original carb and intake, which I'm sure I'll get for a steal, I'm going to pull them, get a Hygrade rebuild kit, and after reading up on here, I'm going to do the mechanical secondary mod.
think that will significantly affect my fuel milage if I keep my foot out of it? (Yeah right lol...)
Besides that, the PO decided to replace the clutch, and NOT the throw out bearing, I can't possibly imagine why...
So now it's making noise, and I'm having to jam my poor transmission into gear, so that's next.
After that, I plan on putting some additive in my LSD, new bushings and shocks/ springs, it sags on the driver side... racing leather buckets, recovering door panels, subs, ect ect.
So in case anyone is curious, I think I've formulated my plan.
My local used car parts lot, (like pull-a-part) has a 7 (Not sure what year) sitting with an original carb and intake, which I'm sure I'll get for a steal, I'm going to pull them, get a Hygrade rebuild kit, and after reading up on here, I'm going to do the mechanical secondary mod.
think that will significantly affect my fuel milage if I keep my foot out of it? (Yeah right lol...)
Besides that, the PO decided to replace the clutch, and NOT the throw out bearing, I can't possibly imagine why...
So now it's making noise, and I'm having to jam my poor transmission into gear, so that's next.After that, I plan on putting some additive in my LSD, new bushings and shocks/ springs, it sags on the driver side... racing leather buckets, recovering door panels, subs, ect ect.
10-21-15, 10:19 AM
#20
Waffles - hmmm good
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Ray, I never claimed I got 28mpg on the Dell, ever. I got 24 mpg HW and about 17 CITY and about 12mpg in the mountains. LOL.
My understanding is the SA intake flows better as well, besides the missing flapper. Ray you
should hang onto that intake if you want me to make you a hogged out nikki. The two will
go together in my mind.
My understanding is the SA intake flows better as well, besides the missing flapper. Ray you
should hang onto that intake if you want me to make you a hogged out nikki. The two will
go together in my mind.
10-21-15, 10:36 AM
#21
Rotospectre, the flappy thing is a butterfly valve that closes fuel flow to the rear rotor when you let off the gas and de-accelerate the engine. Its purpose is to reduce unnecessary fuel consumption and emissions, but it can also cause headaches when it's not working correctly (the shutter valve that operates the flapper messes up) and some claim the even when working correctly it causes premature rear rotor failure because along with the fuel it cuts off oil lubrication to the rear rotor. A lot of people, including me, just wire it open and forget about it.
Sounds like an excellent plan with the pull-a-part Nikki and manifold, nice find! You might want to also check out the GP Sorenson Nikki rebuild kit, these are usually available at the local parts store for $30 or less and they are of good quality, recommended by many.
And don't forget when you get your Nikki in and everything running right you can sell your IDA and manifold for a big profit!
Tim I'm just kidding you about the Del Horto gas mileage, I know you get all riled up whenever I mention your Del Hortos.
On the SA intake, I went out to the parts shed and did a head count on my stock 12A intake manifolds. Sadly they all have the flapper, so nothing from an SA, but the good news is I counted at least eight of them out there, so I should be good to go on intake manifolds for the foreseeable future. Tim, do you think a flapper intake will work with the hogged Nikki?
Sounds like an excellent plan with the pull-a-part Nikki and manifold, nice find! You might want to also check out the GP Sorenson Nikki rebuild kit, these are usually available at the local parts store for $30 or less and they are of good quality, recommended by many.
And don't forget when you get your Nikki in and everything running right you can sell your IDA and manifold for a big profit!
Tim I'm just kidding you about the Del Horto gas mileage, I know you get all riled up whenever I mention your Del Hortos.
On the SA intake, I went out to the parts shed and did a head count on my stock 12A intake manifolds. Sadly they all have the flapper, so nothing from an SA, but the good news is I counted at least eight of them out there, so I should be good to go on intake manifolds for the foreseeable future. Tim, do you think a flapper intake will work with the hogged Nikki?
Last edited by ray green; 10-21-15 at 10:40 AM.
10-21-15, 11:26 AM
#23
Keep the stock needles and seats. Do not install the aftermarket needles and seats from the kit. Do not adjust the floats.
There is a lot more but those are the basics.
I like to spend a good long time tearing a carb down. Sometimes an hour. I use an impact screwdriver because it works and doesn't destroy the screw heads like the common "shadetree mechanic" vicegrip method that some on here will tell you to do.
You do need to reuse many of the screws.
You don't need to remove the banjo bolts or mess around with the strainers inside unless they are clogged. And then it's easy to damage the fine pitch threads in the carb's top. So for now it's best to leave them alone.
You mentioned mechanical secondaries. You will want to do the accel pump mod. I've written about it elsewhere on this forum but I'll give you some fast tips, in no particular order. This is the short version for noobs.
Fill the secondary long slows with solder and reinstall, as they are only necessary for vacuum secondaries and must be filled to prevent a bog with mechanical secondaries. Fill the primary short slows with solder. Drill them to 118 or 1.18mm or .0465" (this is a fairly common drill bit) and install back in the primary side, as these are necessary to make smaller when you remove the choke flap, but are simply way too big from the factory* and make the carbs more difficult to start regardless. Leave the short slow nickel plated 60s in the secondary side alone as they are necessary for an anti-siphon effect, otherwise you could get flooding.
*or you could buy these off of eBay and swap into your primary side. They fit the primary side only as they install too deeply in the secondary side. This is 115 and should work (there is also a 120 available): Genuine Mikuni CV Size 115 Air Jet B42 55 115 | eBay
Leave the main air bleeds, both primary and secondary alone for now. The sizes are 70 pri and 140 sec. I like to modify my secondary main air bleeds to accept some Hitachi pilot jets drilled to 80 for boost prepping but the primaries must be left alone whether boosted or NA. I've tried all the sizes Nikki ever sold ranging from 60, 70, 80 and 90, and found the 70 to be the perfect size. 60 was way too small and ran kinda glitchy. 80 was better than 90, and 90 was terrible. But for now, you can leave yours alone. I'm sure with the solder filled long slows and the accel pump mod, you shouldn't get a bog when you open the secondaries from 4k and up. However if you don't want a bog ever, there is more you must do, but that's too much for this post.
Getting back to the accel pump mod, you need to drill the accel pump nozzle and banjo bolt with your 118 drill bit. I prefer smaller on a carb with stock primary venturis, but without a set of micro drillbits, you pretty much have to use what you have without going any bigger than .0465". You'll see others like Sterling recommend .050" but that's way too big.
As for the accel pump diaphragm and its housing, you need to cut out six pieces of gasket paper the same thickness and size as the diaphragm (I use the gray paper from most auto parts stores). Get longer screws the same thread pitch but with a thread length of 16mm. I don't recall the thread pitch right now. Could be 4mm x .7?
Cut out a piece of 16 gauge steel, drill it at 1 1/4" hole spacing and slot/oval at least one of the holes (I do both for more adjustability). Bend the ends a bit until it fits properly. Stretch the spring that pushes against the diaphragm to about 1/4 longer (be careful, don't over stretch and ruin it) and also stretch the long spring on the push rod 1/4" to 1/2" (be careful, don't over stretch and ruin it). Install the strip of steel with an 8-32 screw and an 11/32 nut with a lock washer and a flat washer or two.
This was the short version. A lot to take in, but if you do it right, there shouldn't be a bog, or very much of one. The way I do it on my hogged out boost prepped carbs is a little different and a little more complicated, and never gets a bog. I can floor it at 2k and it doesn't bog. It doesn't add any power down there, but it doesn't bog. I wait until 3k usually and it's great.
There is a lot more but those are the basics.
I like to spend a good long time tearing a carb down. Sometimes an hour. I use an impact screwdriver because it works and doesn't destroy the screw heads like the common "shadetree mechanic" vicegrip method that some on here will tell you to do.
You do need to reuse many of the screws.You don't need to remove the banjo bolts or mess around with the strainers inside unless they are clogged. And then it's easy to damage the fine pitch threads in the carb's top. So for now it's best to leave them alone.
You mentioned mechanical secondaries. You will want to do the accel pump mod. I've written about it elsewhere on this forum but I'll give you some fast tips, in no particular order. This is the short version for noobs.
Fill the secondary long slows with solder and reinstall, as they are only necessary for vacuum secondaries and must be filled to prevent a bog with mechanical secondaries. Fill the primary short slows with solder. Drill them to 118 or 1.18mm or .0465" (this is a fairly common drill bit) and install back in the primary side, as these are necessary to make smaller when you remove the choke flap, but are simply way too big from the factory* and make the carbs more difficult to start regardless. Leave the short slow nickel plated 60s in the secondary side alone as they are necessary for an anti-siphon effect, otherwise you could get flooding.*or you could buy these off of eBay and swap into your primary side. They fit the primary side only as they install too deeply in the secondary side. This is 115 and should work (there is also a 120 available): Genuine Mikuni CV Size 115 Air Jet B42 55 115 | eBay
Leave the main air bleeds, both primary and secondary alone for now. The sizes are 70 pri and 140 sec. I like to modify my secondary main air bleeds to accept some Hitachi pilot jets drilled to 80 for boost prepping but the primaries must be left alone whether boosted or NA. I've tried all the sizes Nikki ever sold ranging from 60, 70, 80 and 90, and found the 70 to be the perfect size. 60 was way too small and ran kinda glitchy. 80 was better than 90, and 90 was terrible. But for now, you can leave yours alone. I'm sure with the solder filled long slows and the accel pump mod, you shouldn't get a bog when you open the secondaries from 4k and up. However if you don't want a bog ever, there is more you must do, but that's too much for this post.
Getting back to the accel pump mod, you need to drill the accel pump nozzle and banjo bolt with your 118 drill bit. I prefer smaller on a carb with stock primary venturis, but without a set of micro drillbits, you pretty much have to use what you have without going any bigger than .0465". You'll see others like Sterling recommend .050" but that's way too big.
As for the accel pump diaphragm and its housing, you need to cut out six pieces of gasket paper the same thickness and size as the diaphragm (I use the gray paper from most auto parts stores). Get longer screws the same thread pitch but with a thread length of 16mm. I don't recall the thread pitch right now. Could be 4mm x .7?
Cut out a piece of 16 gauge steel, drill it at 1 1/4" hole spacing and slot/oval at least one of the holes (I do both for more adjustability). Bend the ends a bit until it fits properly. Stretch the spring that pushes against the diaphragm to about 1/4 longer (be careful, don't over stretch and ruin it) and also stretch the long spring on the push rod 1/4" to 1/2" (be careful, don't over stretch and ruin it). Install the strip of steel with an 8-32 screw and an 11/32 nut with a lock washer and a flat washer or two.
This was the short version. A lot to take in, but if you do it right, there shouldn't be a bog, or very much of one. The way I do it on my hogged out boost prepped carbs is a little different and a little more complicated, and never gets a bog. I can floor it at 2k and it doesn't bog. It doesn't add any power down there, but it doesn't bog.
I wait until 3k usually and it's great.
10-21-15, 02:42 PM
#25
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we have learned why those (and a couple others) are such a PITA, they are JIS screws, which means they are designed to take a JDM screw driver. not making that up!