I just rebuilt my 84 carb and also put on my 79 intake manifold. I also did sterlings mechanical secondaries mod. The car idles very well now with way less backfiring and it seems much faster on the highway. However, I wonder if the gasket material I used for the ap mod was too thick, or maybe my ap lever extension is not right. I know a small bog is going to happen when the secondaries open, which does not bother me (I kind of like when they open up on the highway) However, I get a bog when I am starting in first gear, and I have stalled it a few times. Only if I take off in first gear very slowly or if I rev it before then it is fine. Do you guys think that maybe I am getting too much gas from the ap and this is causing the bog?

Also, when I give it gas with the car not moving I can see vapour come out of the 2 primaries and then only one of the secondaries (the one closest to the front of the car). Is this normal, as I cleaned the carb very well, although I never took off those jets (or whatever they are called) as the book never says too and I was not sure if they came out. I did however blow every hole with the air compressor.

Thanks, and sorry about the long post.

 

It sounds like your AP is pushing too much volume. You need to back the nut off a bit. Remember; The extension has to be bent to accomidate the linkage timing correctly.
Previously while still stock, the AP began as the throttle was opened, but ended before the throttle was WOT. Our objective was to keep a steady stream through the whole range of throttle motion all the way to WOT. But we did'nt want so much to increase the flow; just keep the same flow rate but over a longer stroke.
If you're dropping too much fuel in there, you're choking it out.

I'm not quite sure I understand what you mean about "vapor". But all of the air bleeds can be removed for cleaning. The four main air bleeds have important emulsion tubes on them with holes drilled cross thru them. These need to be clean, and varnish could have gummed one up.

If I could see a picture, that would be great.

 

I tried backing off the nut as much as possible and it still bogs. I will try to get a picture of my extension, although I am pretty sure I made it correctly. Maybe I should try to take out a few of the gaskets. It could be that I am just used to pushing the pedal down too far and I am getting too much air when the secondaries open. I also tried to tighten the nut as much as possible but the same thing happened. I think I might take off the ap extension to see if that makes a difference and if it does then I will try to make it a little better. Also, it seemed that I was pushing the ap alot and I was a little worried about breaking it. I like the mod, in every gear it is just starting off in first that bothers me, as I have stalled it a few times.

By vapor I meant gas. Do I have to take out the carb again to take out the emulsion tubes? The haynes book does not say anthing about it.

 

No you don't need to remove the carb, but to access them you'll need to take the top off.

Though I have'nt read through my write-up recently, perhaps I had'nt stressed that fact that you'll need to "learn to drive" your car all over again. You need to feel the carburetors need. You now have total control with your foot, and you need to practice some finess. You CANNOT tromp the pedal, and expect good results. It is not a Dodge Ram truck!

Feed the carb like it were a baby...not too much too fast.

Try setting the AP for optimized 40-60 fourth gear power punch. Then see if you can learn the finess needed to burn rubber in first without dumping @ 4K!

You'll know when you get it, cause it'll FEEL outstanding!

If this does'nt work for you, then perhaps you should decrease the AP volume, or "Undo" the AP mod all together.
I have a feeling once you get used to it, you'll want to keep it.
But you can't get used to it until you tune it properly. So get it working right for chirping in third upshifts.

Are you running larger main jets at all?

 

Hey what is a sterling mod?

 

It's an absolute must if you have a Nikki carb. Read about it here: Carb Crap...Nikki Mods

 

I agree. Its a world of difference.

 

No, I just used the stock jets that came with the rebuild kit. Do you think larger jets would make a big difference?

Just a few hours ago I got on my Carter fuel pump and Holley regulator. I never had time to play with the regulator yet (I also have no gauge) and I didn't really drive it around a lot yet, but I think there is now less of a bog.

Also, Mar3 was right! I never would have thought I could hear the pump over my exhaust as I have header to ceramic glass pack to dynomax super turbo to a dual resonated tip. I might as well just get rid of my stereo because now I can hear my exhaust and my fuel pump with the stereo on and I have a 12" sub! I used the rubber bushings that go in between the pump and the bracket but I guess I should have used some in between the bracket and the frame also. My car does feel a lot faster now, and will probably be even better when I can get it tuned a little better.

 

Also, where would I get larger jets from? I think I remember people saying Mazdatrix has them.

 

Yeah, the carter is loud. I've read about people wrapping it in rubber (like inner tube material, I would imagine) in an effort to quiet it down with a bit of success.

If you have the Holley 4 psi reg, then you're fine...IE, you're not going to blow the needles out of the seats. But you won't get the float drop correct if you can't "see" what you're doing - and by "see", I mean you need to know a reference point to dial in your pressure.

Fuel pressure is a very important setting on your carb. It dictates how the carb will transition throughout the RPM range. It will set your power band to it's optimum for the load it sees the most. Do a search.

The jets are available at Mazdatrix. But you can drill out jets from another Nikki if you happen to have one kicking around.
I DO NOT suggest attempting to drill the original jets. I'm a big proponent of keeping the original crap on hand just in case **** does'nt work out. You can then, with confidence, always put it back the way it was.


82 transam, did you also do the AP mod? How did that work for you?

 

Actually, I realized I made a mistake when I mounted the carter as I put the rubber inbetween the pump and the bracket, and what I should have done was put the rubber inbetween the bracket so no ends are touching metal. Now I have the nuts on the top vibrating and that is probably why mine is soo loud. What is a good cheap pressure guage to buy? I know your suppose to get one from Yaw but I don't think I will do that. Does someone know what the HOlley 1-4 psi regulator comes set at when you buy it because I just put it on and did not adjust anything.

Also, how big should I try to drill the jets out (I have 3 carbs in totall to play with) the jets you are talking about are the ones that you get to from the float bowl right? (Sorry I don't have my Haynes with me and this was my first carb rebuild) Also, thought Peejay said it is not good to drill out your own jets?

Do you think doing this will get me a good amount of hp or should I be looking for an aftermarket carb. I would be happy if my car would be in the low to mid 15's. What do you think my car would be putting out now if I was perfectly tuned.

I have on my 85 GS:
header>glasspack>2 1/4 pipe >dynomax super turbo
Carter fuel pump holley regulator
mechanical secondaries ap mod
79 intake manifold with no emissions controls
removed air pump
homemade cold air with K&N

Also, I took some pictures of my ap extension, so I will try to post them later this week.

 

I don't think there's anything wrong with the gauges that are on the market if you get one with the understanding that it will most likely be #1- Not correctly calibrated, and #2- the percentage that it is off by may increase with pressure!
Yaw sells gauges that come from a measuring instrument company. I don't know how pressure gauges work exactly (I imagine there is a diaphragm that pushes against a radial spring w/the needle attached?), but more importantly, I don't know why it seems so difficult to produce accurate gauges. It is not really necessary to buy an accurate gauge like the one Paul Yaw offers, as they are expensive. You just need a "reference point" so that you can increase or decrease the pressure in small, (relatively) equal increments for tuning purposes.
Gauge accuracy is a necessity for racing crews that need to keep a log of the ideal carb settings that are different for each race track (elevation differences, temperature, ect).
Gauge accuracy is not so important for us street runners. We simply need to know where we had the regulator set before. The street runner typically tunes using his ***-o-meter, a stop watch, or his G-Tech anyway.

There's no telling if they all come from the factory set the same way. I just went out and fucked around with mine to see if I would be able to tell you the "PSI per ROTATION" change it makes. But as I kinda remembered, it is'nt linear...IE, when it first makes contact with the spring (take allen stud all the way out, put it back & turn it till it touches) it takes three revolutions of the stud to increase one psi. (It starts out at 1/2 psi, not zero. so it took 3 turns from just touching the spring to get to 1.5 psi) but then it dramatically gets more sensitive, to a point where it only takes 1/8 turn to increase 1/2 psi!

Hate to tell ya, but without a gauge, yer tuning her with blind shots in the dark. And as I had written earlier something to the effect that you would be fine for now because the regulator only goes to 4 psi...WRONG! I managed to get mine up to 5.5 psi with it all the way in just now!
I suggest you turn it in so that the lock nut is flush with the allen stud, and then back it off about 1/2 turn. This should be a good starting point for you. Just remember when you start making runs to adjust it that you're at a sensitive point where 1/8th turn will mean a significant pressure change.

Get a gauge-any gauge!


I don't know how big. I got my jets from Yaw with my carb, and I've never measured them. They are numbered, but I don't think it's the thousandths measure.
I will try to remember to measure some to see.

Yes, the "main jets", or "fuel jets" are the two that are in each float bowl. Remember, the secondaries require the slightly larger jets!

Peejay is right. It's usually not good practice to try to drill out your own jets without either a tiny lathe, or a drill press. Three problems confront the inexperienced...#1, If the drill bit is not razor sharp (Read: Brand New!), then scoring of the inside of the jet walls can impede flow. You would'nt think it, and you might not even notice the scoring without a magnifying glass. #2, If the drill does'nt come straight down perfectly, this can make the hole either skewed, or out-of-round. The fuel won't be metered exactly like the other jet.
#3, and the most common (I imagine) problem would be that the jet ends up with a slight burr that substantially impedes flow.
Any of these things can be a minor flow impediment that could become much worse at higher flow rates.
However, if the "home jetter" is aware of these dangers, he can, with some practice, avoid them.


Don't want to burst your bubble, but maxing out the fuel flow of the stock Nikki won't get you pulling low 15s. With the increase of fuel volume to the carb, and the increase in jets, you'll be giving the carb all the fuel it can take for the amount of air going thru it. You can't give it a whole lot more fuel cause you can't give it more air!
This is where major modification comes in, like opening up the venturis. You have everything else just right...right down to the best manifold choice. But with the size venturis you now have, the carb becomes your bottle neck, and there's nothing you can do short of either modding the venturis, or getting a bigger breather.
However, you may just pull a sixteen; I don't know.
You're looking at about 135 HP tuned well with what you have now.

You should use the Nikki as a learning experience to familiarize yourself with what changes do what to the power curve of your baby. Then it's time to explore your performance carb options!

You should'nt feel bad, though. You are one of the FEW people who have done this the "right" way...You went and got the bigger pump and regulator, exhaust, better intake manifold, ect before looking at performance carbs.
Most guys go get the carb, and are disappointed to have to shell out nearly as much money again just to get it to perform to its potential.

I've taken enough of your reading time!!!
Let us know how it goes.

 

No I didn't. After doing the mechanical secondaries mod i was really surprised the first time i mashed the gas. I never thought it would make that big of a difference. As for the AP mod, ever thought of taking some pics to go along with that writeup? Guess I'm a visual person cause I didn't get how to do the mech secondaries mod till innitab helped me out. I would like to do the AP mod, it needs it. I assume it helps to get rid of the slight studder when you slam on the gas.

 

oh yea, one more thing, has anyone done any tests on this mod? Like how much of a speed/power increase there is? just curious

 

I'll have to take some pictures and post them on the archived thread.
I don't know the power increase, and I don't have a lot of feedback...Just a handful of people, but they all said great things about it.
It would be interesting to see what the power gain really is on a stock jetted, stock fed Nikki.

 

I guess I will go out and get a gauge. Also, I didn't expect my car to run low 15's and I think next year I will look for a used carb and manifold. Untill then I will play with the stock nikki. Also, I don't really have much of a bog anymore since I put in the fuel pump, and the ap nut backed off. I still need to tune it better though.
I also have 2 extra engines (a 79 and 84) and the one in my car. I think this winter I may take the 79 engine apart and try to street port it myself. Who knows it may even run for a while and if it doesn't that is ok.

When I first bought this car 2 years ago I was not even going to mod it as I always thought they were slow seeing that they only have 100 hp stock and weigh 2300. My friend has a extra second gen body and I was looking for an engine for it forever. Then I thought I would buy the 85 for the time being untill I found an engine, and was rather surpised how it ran. ALso, now whenever I drive my friends second gen it just feels too big. Infact, every other car I drive now feels too big.

 

Also, If I were to order jets from Mazdatrix which ones should I get? THey have 24 different sizes. What do you think would work best with my set up? .180 secondaries?

 

I just put on a gauge and it read 4.5 psi. I tried a few runs at 3.5 and 3, however my ***-o-meter is not very accurate and I am having a hard time telling if one is really faster then the other. At first at 3.5 psi it seemed like the high end power was coming on in bursts kind of like on then a little less power then on and so on. (if that makes sense) I also played with my timing a little and it seems better. Now I have it at 3 psi and it seems ok, but I notice that when I shift from second to 3rd I get a wierd small back fire (My car used to backfire like crazy with the old manifold and the shutter valve, but this is a different backfire sound.) It is kind of like a second gen backfire sound. Around what psi should I set the gauge with the small mods that I have?

 

It's gonna make less a difference until you get bigger jets in there. Then the pressure setting will show dramatic changes.
This is covered in bits and pieces in old threads, but if I give you my take on it all in one (long) post, it'll be good for future searches - So here goes...

The fuel pressure controls the "float drop rate". Float drop rate can be thought of as how fast the level of the fuel drops down while holding at WOT. This is very important, because as the fuel level drops down, it uncovers holes in the emulsion tubes at the bottom of the air bleeds. This has a dramatic effect on the performance of your carb because it, combined with the number of holes in the tubes, as well as the size of the air bleeds will dictate what your air - fuel ratio is at any given point.
Fuel pressures and air bleed sizes are changed for different race tracks because of elevation changes and air temperatures. But they are also changed so that the mixture will be richer at certain engine RPMs for tracks that have alot of climbing involved.
The setting that's ideal for a level straight away is too lean for the loaded-engine requirements of going up a 15* slope.

For your application right now, you've pretty much done all you can do to maximize your current fuel jets. A lower setting will cause the fuel in the bowls to drop down uncovering the emulsion tubes and lean the mixture a bit at the high end, You won't notice the effects until you reach the upper RPM band.
You can only drop it so low before the incoming fuel is then not adequate enough to replace the volume that is passing thru the jets. At such low pressures, you'll lean out severly, and quickly. (We are talking REALLY low pressure, here!)

Installation of larger fuel jets means that the fuel level will drop a bit quicker. If it drops quiker, then the change that the emulsion tubes have on the mixture will occur at a slightly lower RPM. This is corrected by going to smaller airbleeds, or ones with a different emulsion tube cross-drilled configuration.This is something you really don't have to be concerned about until you port venturis, ect.

As far as what pressure you should set it at now, I would say anywhere from 1.75 to 3.75 psi. You will notice dramatic results only in the higher RPMs and most likely more at the lower pressure settings.
Start out low, and raise it in increments of 1/2 psi. You'll come to a point where the previous changes made little difference, and then BAM, there's a BIG difference. Then you might go back 1/4, and fine tune it like that.
Unless you're a stopwatch junkie, 1/8th psi changes will seem not to makle much difference. But you want to feed the carb enough to scream happily, yet not starve it, and most importantly, not drown it.
The best feature of the carb that even makes it a workable fuel/air metering system is the emulsion tube. Gain an understanding of what's going on in there with regards to fuel level drop rates, the uncovering of the emulsion tube holes and resultant induction of air into the fuel before it is even drawn out through the booster venturi.


As far as the choice of jets, I have faith that the good folks at Mazdatrix can suggest the best size jets for you. In my opinion, you should have at least three complete sets that are right around the "theoretical ideal" size. They may suggest the very same thing, so don't think that they are just trying to make a sale.
Be sure to tell them your whole set-up. If you get the impression that there's a pimple-faced "EFI-Kid" at the other end of the phone who does'nt know his ****, then perhaps you should do research here and on Mazspeed and find out what they suggest.
However, I don't think the jets are very expensive.

I should know (find out) because I tend to dull out alot of Nikki carb help. The reason I don't is because I'm running a Yaw modified carb that I've even further modified myself. The result is something barely recognizable as a Nikki carb! I use stock primary air bleeds, large secondary air bleeds with modded E tubes, different idle air bleeds, and huge fuel jets. I get exactly 12.5 MPG with all my shifts @ 7+K RPM. My "happy spot" starts at 4800 RPMs and pulls strong like it wants to self destruct all the way up!
Below 4.8K, she drives like a regular old car!

 

Let us know when you get some pics. I'd like to try it. I'm surprised more people haven't tried it, its very easy to do.