Qingdao

iTrader: (3)

I STRONGLY seafoamed the car, and with the 127 jets it was PERFECT except for idle. PIG rich extreme. like driving with a choke circuit open on a Mikuni. No amount of screwing that little *** in did any good. So I put my 118 jets back in. And lean on cruise back where I started, but I can do anywhere between 10-14 on idle if I wish.

I just ordered a crapload of bits from a few manufactures on ebay. I figure with all the kits I just got I should have a better selection of bits to choose from. I want to try 121 like Jeff wrote.



EDIT: Erick your inbox is full.

Qingdao

iTrader: (3)

So I got to the bottom of my lean issue. I used a FB 84' main body and a 79' top. They bolt together and the bowl surface looked similar. BUT they are different. The 84' body has a hole in the off idle circuit in the middle of the carb (i'm assuming it is for some kind of FB emissions thing). The 79' top doesn't have this hole. This explains why regardless of how small an air bleed I used off idle throttle was always lean. I am now using a .94 short slow air bleed.

Now to getting the ratio's a bit above 10.5 during WOT in the primaries.

t_g_farrell

iTrader: (1)

I think a good rule of thumb here is to not mix carb parts from various years. Obviously Mazda
was tweaking and changing things over the years, as you have found out.

Jeff20B

iTrader: (13)

The problem with the 79 top is how it doesn't shroud the primary air bleeds. This allows a straight shot of compressed air to force its way into the primary circuit. Leans it out too much.

I had a similar problem to yours when I tested a couple of 79 carbs with the turbo. Totally leaned out the primary circuit. It was scary. I saw 17 and leaner on the wideband! My conclusion at the time was 79-80 or SA carbs just don't like boost and left it at that, and concentrated only on 81-85 carbs which handled boost far better.

If you study the shrouded area of an 81-85 top you'll see what I'm talking about. It's a nice little pocket to protect the area above the primary air bleeds from directly incoming air. Does that make sense?

You also need to use 70 air bleeds, which happen to be from 81-85 carbs. The 60s are too small and run kinda glitchy. I tried 80s which were better than the SA 90s. Those were terrible and not recommended even for NA carbs. Since then I've machined a couple sets of 90s to accept some Hitachi pilot jets drilled to .68 (closest size I have to 70 without going over, which I also used to drill all of my 60 air bleeds with success).

When I installed a set of the modded 90s with 68 drilled pilot jets in a 79 carb, they are really tall and are very close to the lower edge of the SA top. I don't like how this looks so I've decided to test a set in an FB carb instead, to see if the fully shrouded area will be a benefit. Just waiting for nice weather now.

Qingdao

iTrader: (3)

I'll snap some pics next time I tweek it, but for the moment the .22 hollow point bullet is keeping any air from moving in the little hole I'm talking about. And its running perfectly. I think the richness on WOT is from the accelerator pump. I'll have to drive it up a big long hill soon.

Jeff20B

iTrader: (13)

I'd like to see your weird bullet solution.

I have some more data to add to the pile. I tested two 79 tops on an 81-85 main body today. This was to test some sets of OEM needles and seats to make sure the floats were correct. I only test ran them. I didn't actually drive it.

Two things I noticed. 1) Just test running, the double decker modded 90 air bleeds that had a set of 68 drilled pilot jets in them, were just fine being super close to the 79's top. 2) The altitude compensator circuit's two holes in the castings of all 81-85 main bodies (US-spec) that are right next to the primary boosters and divide the primary side of the carb from the secondary side of the carb, are not properly blocked by the 79 gasket so there was a little sliver of area for air to come in and it leaned out my idle a little bit. We're talking the difference between 11.6 to 12.2, as that was where I had to adjust it to (12.2), to compensate for the unwanted air. Then when I swapped the 81-85 top back on, it went rich (11.6). Kinda interesting. And that was from a tiny sliver of area. I'd imagine if the 79 gasket was cut a little differently or warped due to age, I'd have a whole lot more unwanted air to deal with, as you probably did Qingdao. This might be why Paul Yaw would take the extra steel ***** that come in some rebuild kits and hammer them into the holes in the main body. This is a problem for anyone who has to tear down a Nikki for cleaning though because now you have these long drilled channels that it is rather difficult to get the water out of. That is why I recommend solder filling the little brass 40 air bleed up under the air horn and removing the altitude compensator and blocking the area with a plate of aluminum. Some just smear JB weld but that looks stupid and can flake off. And again the plate can be removed for cleaning while the JB weld pretty much can't.

Qingdao

iTrader: (3)

Its just the bullet, not the cartridge. I'm dumb, but not that dumb

I had a few rolling around in the car when I noticed the holes, and figured lead is easy to shape and soft enough to plug a hole yet be removable. why not?

Qingdao

iTrader: (3)

I popped back in the nikki today to try out some .84 air bleeds, and reinforce the holes.

These are the holes on the '84 body that will lead to massive off idle lean issues. And those are the shaped .22 slugs. I put some JB weld in it to seal it up but the taped (or peened in?) in lead held up for over 100 miles of running around.


And just out of curiosity does anybody know what the numbers stamped in the boosters mean? I've got 880 on the secondaries and 542 on the primaries.

Jeff20B

iTrader: (13)

I leave those alt comp holes alone and just solder fill the little 40 air bleed under the air horn. I also remove and block off the alt comp with a 1/4" aluminum plate and a stock gasket with the stock screws.

You'll notice your globs of JB weld will interfere with your gasket.

The numbers were just part numbers from the Nikki manufacturing plant. My rare 6 port Nikki has different numbers because the boosters were different parts with different sizes from our common ones.

workaholic

Is it possible to do this mod, but keep vacuum operated secondaries? Or is it not recommended. I am uncertain about running mech sec; tryna find the balance between go fast and streetability.

Jeff20B

iTrader: (13)

Vac sec not recommended. Oh and streetability of mech sec is better than stock if you do the mods correctly.

We need to let go of ALL preconceived notions here, and this is one way to do it.

I don't think I could even drive a stock vac sec Nikki anymore, and why would I want to? They're terrible. No wonder so many people went to aftermarket carbs over the years. But now the Nikki is back with a vengeance.

workaholic

Very good write-up! My carb is coming along decently. I'll post results after it's finished!

Jeff20B

iTrader: (13)

Just remember this thread is very old and many results I showed here have been updated and replaced with better techniques. This thread should be viewed for archival purposes only.