The pilot circuit would be where the car gets fuel in low speed conditions. Teeny tiny jets that clog really easy. I would make sure they are clear because when they clog the car will not get any fuel under low speed besides when the accel pump cycles. I had the same problem with my rx7 only mine is worse now because it sat for the last 3 years. I need to tear down the carb but I don't have the time.

 

Is the pilot circuit milled into the carb body or into the top?

 

Called the "transition circuit" or "low-speed circuit" in Mazda lit.

 

What I'm getting at is should I disassemble my carb, re-soak it in ChemDip, re-rinse it and blow it out with compressed air, and re-assemble?

-Jim

 

Bump!

 

Yes, you need to go through the carb again. I don't bother soaking it unless there is extreme varnish and sludge.

Couple cans of carb clean with the red straw nozzle gets to all the holes well.

 

Hmm that's got to be what's happening to my carb. Coming to stoplights the idle mixture is anywhere from 12.3:1 at one light to 14.4:1 at the next light and initially very very lean from high vacuum throttle let off when coasting. Also when I let off the throttle, it goes lean like 16:1 and has a studder. Makes sense the transition circuit is plugged.

Looks like I'll be ripping the carb off here soon to go through it again! Hope this fixes the issue!

 

So I went back through my carb last night. Pulled it apart, hit it with carb cleaner (aerosol cans) and 120psi of compressed air. RE-assembled it, cut a new gasket, and went for a drive. No dice, still same issues. Next is to get new bolts for my '85 manifold's block-off plates and swap intake manifolds to see if that cures my issues.

I'm wondering if I'm not getting proper vacuum signal because of my SA manifold mated to an '85 (1480) carb spacer and carb. Could this be possible?

 

Could be; a lot of vacuum routing takes place in that spacer. It's not just straight-thru holes, there are routing channels in the phenolic below the permanent gaskets.

 

Could I cause damage to it by blowing high-pressure air through the vacuum ports that go to the rats nest?

 

No damage by clearing holes out. There is still something weird if your AP bowl isn't filling.


I've got a SA manifold under a '82 GSL Nikki. I forget which spacer I used, I think I used the SA spacer as the holes lined up but this was two years ago I don't remember. No rats nest, PCV hooked up, and about 6months after then install I have your symptoms.

It really seems like it's an issue on how the vacuum signal in the manifold is working the transition circuit. Mine is GREAT with a little bit of load and anywhere on the freeway. But in town cruising say 25mph in first, second, or third gear it misses and studders and I have weird lean spots verified by my wideband.

 

Ya, the AP bowl is not filling at all.

Your spacer (i just found this out) should have the part number molded into its upper area. Mine is a 1480, which is correct for my carb, but not for my manifold.

I may have time to swap out intake manifolds and cut a new cork gasket for it tonight.

Thanks for the input, I'm glad that someone else has had similar issues.

 

The spacer doesn't explain the no filling in the AP bowl.

You should be able to turn the key on, let the fuel pump run. Then work the throttle and see fuel squirt from the nozzle. Unless the weights are under the check *****.

 

I made sure that the weights were on top of the check ***** when I was cleaning out the carb last night.

I did that before driving it last night and the AP won't fill with fuel.

 

I'm pretty sure I received a bad AP diaphragm with my rebuild kit. I'll be probably ordering a new one this week.

 

At the risk of making myself sound like a bigger idiot... I recall one time that I installed my AP diaphragm backwards, with the 'stem' pointing into the carb instead of towards the actuating lever.

It fits fine that way, seals fine, the stem even nicely holds the diaphragm spring for you... but it doesn't pump fuel.

Not sayin', just sayin'...

 

I thought I did that, and have made sure that it isn't installed backwards a few times.

Last night I pulled the AP cover and 1-2oz of fuel dumped out of it, so, for some reason, the AP is now filling with fuel. I pulled the AP nozzles and cleaned them out with music wire and carb cleaner, blew everything out with compressed air, and before re-assembling everything I actuated the AP by hand. I could see fuel around the weight below the AP nozzle, but it wouldn't move as I actuated the AP. I have ordered a new carb rebuild kit, because I'm at a loss. I'm going to replace my AP diaphragm with a new one, because I have a feeling that I may have received a bad diaphragm with my rebuild kit. It should be here tomorrow, and I'll post up results at the end of the weekend.

-Jim

 

Jim, it almost sounds like the inlet ball-and-weight aren't sealing well enough to let the pump raise the fuel to the jets.

Maybe the ball seat is chewed up or has something stuck on it, preventing it from sealing during the pump stroke?

Being small and deep, it's hard to inspect.

 

I had the top of the carb off last night and was actuating the AP by hand and didn't see any fuel being pushed back into the rear fuel bowl. There was fuel up around the weight in the inlet.

 

Can someone post a picture of a "stripped" nikki WITH vacuum secondary diaphragm still in tact? I think Neal (KanseiRotary) may have figured out some of my issues...

 

From which angle?

 

Top? Side? He was saying that if you don't have that on (or the ports blocked off) that you'll induce a vacuum leak that will not allow the accelerator pump to spray fuel into the primary barrels.

 

Not having the vac sec hooked up or blocked will definitely cause a vacuum leak... but the AP does not depend on vacuum.

It will spray even with the engine off , so long as there is fuel in the rear bowl to feed it.

Vacuum secondary unit:


Where it goes:


four holes; three for screws, one (2nd from top) is vacuum.

 

Thanks DD.

I found a good Vacuum Secondary actuator last night and hooked it up. I also discovered a HUGE vacuum leak last night and got that fixed. Now I'm within 1500rpm of having a 1k idle, but my AP is still not working.

I'm expecting my new rebuild kit today, and I'll try and get the new AP diaphragm installed some time tomorrow (helping my parents move to their new house tonight and tomorrow, and leaving for a two week road trip for work on Sunday...).

I can get the engine to increase RPM with VERY slight pressure on the accelerator, but for normal driving it's useless w/o the choke.

-Jim

 

If you need the choke butterfly closed to run, it's getting too much air or not enough fuel.