I know they're 63 in holley airbleed sizes, that is stock secondary jet for most nikkis

 

Jeff, thats not an 83, may look like it but its a 93 trust me. The secs for all 79-80's are 160.

 

jeff i forgot to check last night but i'm going back to shop tonight see what i can find for ya. I'm running 36 and 63's in my car, those are equivelent to nikki sizes. i'll see what we have to spare and get back to ya.

 

Carl, thank you! That means the other Hitachi has 160s in the secondaries and it's decent up to about 7k even on a streetport. Cool! I can only assume the stock secondaries were 150s because I found one on the PO's garage floor, and the '79-'80 and his Hitachi were the only stock carbs he had messed with in years. The secondary jets he installed in the Hitachi also looked like they had a bit of corrosion on them, which actually matched the primaries in the '79-'80 carb. I'm going from memory here, but this is some great info because it means I don't have to take the top off that carb for now. It's in my daily driver, so I worry wenever I have to mess around with it (the accelerator pump is not fun to deal with on the Hitachi due to it being part of the top of the carb).

150 is awfully close in size to the 145s I took out of my Hitachi (which has always felt weak at high RPM compared the the other one). Using that logic, I could also assume the primaries of the other Hitachi were 100s because mine were 94s. The primary circuit of the other Hitachi felt tons more powerful than mine when both were tested on the same engine, but transitioning from primary to secondary felt different. You see, the other Hitachi has such a powerful primary circuit that when the secondaries kick in, the difference isn't as abrupt and powerful as it is on the weaker Hitachi. Yep, the weaker Hitachi feels like it's got more power when the secondaries open simply because the difference is so great. What a sneaky way to trick somebody into thinking the weaker Hitachi is actually more powerful. Perhaps 160 was a tad too large? Or maybe I'm feeling the limits of what Hitachis with everything stock, other than the main jets, is capable of?

Man, I think I'll go with my gut and only up the jet sizes by 10 each. That means 105 primary (because 104 isn't available) and 155 since I have a set in a '73 (somewhat water damamged) Nikki sitting here. All I'd need to buy are two 105s from Mazdatrix (which is more than I can afford at this particular moment lol).

I assume since 94 was a bit lean, that 100 would be spot-on stoich, and 105 would be a tad on the rich side (for safety). Then the 155s for secondaries could be upped without a problem since I've got both sizes to choose from. Yeah, no need to jump into 160s and risk a slightly weak feeling seconday circuit, all other aspects being equal (air bleeds etc), right?

Someday after something else is running (Cosmo), I'll pull the tops off of both Hitachis and maybe even my ancient '74 Hitachi as well and write down everything and note any differences. Then again, my Cosmo also has an Hitachi! Oh man, that's four Hitachis and I thought I had a lot of Nikkis (seven), hehe.

36 and 63 are equivilant to Nikki sizes? Is it some sort of standard to metric conversion thing that's screwing me up?

Carl, the jets in the '79-'80 (it has a large primary air horn, so that's how I could tell) were covered in white aluminum corrosion so I wire wheeled them for a few seconds until they were still dark brass, but clean. I'll get out some high powered magnifying lenses and some really bright light and see what I can see. If I can take a close up picture, either with a digital camera, or the B&W securty camera (remember those black and white pictures I used to post?), I'll post it to let you all see them. Check out these pics to see what the security camera is capable of with a lens in front of it (the color pic of the broken spring is not mine). http://www.nopistons.com/forums/inde...howtopic=35844

 

holley measures in inches and nikki jets are measured in mm or something simlar to that. basically the 160 = 63 and the 94= 36 same size just different unit. if you still in need let me know.

 

Thanks for clearing that up BMS2004.

karism, if I like what the 105s can do, I'll get some 110s and also up the secondaries to 160 and see if it's better or worse.

 

I send the Sterling Carbs out with stock 160s (.062s)in the secondaries, and .058s in the primaries.
But that doesn't mean ****, and need I explain why?...AGAIN?
First the venturis are bored differently, and secondly the emulsion system is also rejetted to make the best use of that fuel jetting configuration....023s in the primaries and .046s in the secondaries.

It all works together, folks.

Y'all need to invest in some drills.
Go to Napa and order Holley Dom inator 10-32 thread air bleeds...a package of ten .023s.
Order from a jewelery supply online store a set of drill bits, and then yer good to go!

 

but then sterling, people would only come to you for consulting and not the actual work....that wouldn't be any good would it? =) well i guess you could start a hotline and charge people money by the minute.

 

This is why I thought the '79-'80 carb had 83s in it. Check out the differences in the number 9.

 

91,92,93...

 

Thinking about it some, everybody says the '79-'80 and older carbs were jetted rich from the factory due to the thermal reactor. Well, according to my recent exploits venturing into carbs, it would appear one jet size bigger equates to a richer jetted carb. Say what? Just one size doesn't seem like much at all. I'm sure the air bleeds etc are different, and I could run out to the garage and write down all the numbers and compare them, but I'm sure you guys already know them.

What do I need to do? Hitachis are different yet kinda similar to Nikkis. I fear the info Sterling can offer might be like comparing the oil pump chain on a rotary to the timing chain of a piston engine. They're both chains.

Ok, I could get a set of 95s which would be one size bigger than my stock 94s. Should I move up in such a small step? How about 100? 105? 110?

I feel so carb-stupid right now.

 

I looked inside my water damaged '74 Hitachi and it's got 106 primaries and 140 secondaries. 106! Holy Holley! Ahem. The '74 appears to be rebuildable, which is seriously excellent as I'm actually one carb short at the moment (I built an R5 13B from spare parts for my REPU and have been sharing a carb with my MG project).

Carl, the air bleeds of this '74 are rather different from any Nikki I've ever seen. I apprecuiate your help, but I feel like I'm kinda on my own at this point. I think I'll got some 110s for the primaries and maybe install the 145s from the '77 Hitachi. Meh, I don't know what I'll do yet.

 

Scroll down to see part of a Hitachi. http://members.tripod.com/~grannys/4rotor.html

 

Nah, not a chance. Once they get frustrated trying to get it right, they'll realize what a bargain we really are. We've invested many hours (like in the hundreds) figuring all this stuff out. Whats your time worth to you?

 

BTW, Hitachi MAKES [/i] Nikki[/i].

 

Yes, and lots of other hot stuff.

I'm in the process of rebuilding...

 

'77 from 94 to 106 and 145 to 160
'74 from 106 to 110 and 140 to 155

 

What, are you using this thread as your jet change log?

 

Might as well.

 

The 106s in the primaries of the '77 carb are very nice! This engine has never felt this powerful on the butt dyno before. It looks like I'll have to get a set of 105s soon (see '71-'85 RB catalogue, page 16).

As for the secondaries, this is where it gets kinda grey. I installed the 155s and I don't know if that's killing the power or improving it. Infact, as I was testdriving it, it's as if there were three positions in the gas pedal: normal, medium, and holy crap! I can only assume the secondaries are opening. The only thing I can compare it to is the REPU, which has a definite transition. In this car however, the farther I press the pedal down, the more power is produced without a normal sounding secondary transition. Are they opening at all? The forcefulness that I've grown accustomed to isn't really there; probably because the primaries are now quite powerful, yet I did up the jets from 145 to 155 without changing anything else in the secondary circuit. Either way, it actually gets kinda scary because the brakes are bad. The car is also low to the ground so it feels faster than it actually is. An indicated speed of 40mph is like woah!

So what do you think I should do about the secondary jets in the '77 carb? Go back to the stock 145s, stick with the 155s, or maybe even try the 160s? I don't have access to a dyno, and the butt dyno is only marginal at best (I don't know this car very well so the butt dyno probably shouldn't even be used here). I can list the numbers of everything and let you carb experts recommend stuff.

This is how my '76 Cosmo FSM lists Jets and Air bleeds
1. No. 2 secondary Air bleed
2. No. 1 secondary Air bleed
3. Secondary main air bleed
4. Primary main Air bleed
5. Accel. pump injection nozzle, weight and ball
6. Richer air bleed and jet (M/T only)
7. Vacuum jet

This is what the '74 carb has in it
1. no number
2. 150
3. 160
4. 80
5. (no weight inside AC pump squirter, and I don't know why)
6. no number
7. 120

This is what the '77 carb has in it
1. 80
2. 100
3. 100
4. 80
5. (I haven't examined the AC pump squirter on this carb because it squirts fine)
6. 150
7. 90

As you can see, the primary main air bleeds of both carbs are the same size, so logically, they should both be able to use the same size primary fuel jets. In other words, both carbs can take advantage of RB's suggested 105 jets for best power on a '74-'75 13B. This explains why the test drive today was so successful.

As for the secondaries, I really don't know what I should do. I welcome any suggestions based on the numbers I posted above. Even educated guesses are welcome.

 

I would think that a smooth transition between primary and secondary operation would be preferable to a kick in the pants jerk.

As to the '79-'80 carb being jetting richer than the later models, my carb is actually jetted leaner than an '81 carb that I picked up, but the car still runs rich enough to totally blacken my tailpipes. I'm tempted to pull the original carb and fit a rebuilt '81-83 carb on there and give it a whirl.

 

The 13B manifolds have seperate runners while the early 12A ones were also seperate and then had machined channels between primary and secondary runners until '81. Then we got the stupid flapper valve and a manifold that flows even worse. Since the only engines I've got here that actually run are early 13Bs, I am quite used to the jerk and actually really like it. It's fun because it always surprises people who ride with me. My friend's stock 1st gens are always a lot smoother of a transition.

The Hitachis all seem to have closer jet sizes while the Nikkis tend to have a farther spread. Could it have something to do with the channels? Can I install a Sterling carb on an early 12A manifold which lacks the channels?

MosesX605, could the floats be to low? I guess that's a question best answered by Carl.

 

well just guessing here since the secondary air bleeds are smaller than whats recommended, i would say you would go to a smaller jet than what the FSM recommends. I say this for this reasoning. The vacuum signal is not bled off as much with the airbleeds, meaning that more of the vacuum signal is being set to the jets. If you to take a complete stock carb and put much smaller bleeds in it, it would run alot richer because the vacuum is telling the fuel jets to send more fuel because the airbleeds didn't bleed as much of it off.

if your floats are low, more of the emulsion holes are uncovered, which bleeds off more of the vac signal, thus effectively leaning out the carb in a sense.

**don't hold these opinions as truth just my understanding of things.**

 

Well the REALLY early 12A manifolds were 4 seperate runners. Then on the SA's they got the dual plenum. And you know the rest.

I think the Hitatchi jetting is that way cause of the venturi sizes and the airbleeds. True BMS, but remember, airbleeds are most effective at hi rpms. So they are used to "trim" the A/F at the top end once low and midrange are established with fuel jets. And also true about the lower float levels BMS. Actually they will eventually become uncovered as rpm's increase, but a lower float level will allow that to start happening sooner. Again another tool to tune the A/F curve.

 

I have two or three early fully seperate runner 12A manifold ands one or two dual plenum type. I'd assume the dual plenum type is better for a Sterling carb, but it would be cool if the seperate runner type could also be used.

Here's a question for the Banana carb folks. When installing a factory carb on a street ported engine, is it wise to decrease the fuel jet sizes due to the increased vacuum created by the engine at high RPM over stock ports? Or should the jets be increased? I don't want the air horn to act like a choke at high RPM and cause the AF mixture to go pig-rich. What do the air bleeds have to do with the equation? As for air bleeds, do I want bigger or smaller than stock on a streetported engine? Thanks.