12a idle problems
 

1982 Rx-7 GS
80,000 miles

Rats nest Removed
RB Header
Carb Semi Stripped

I have been having problems on getting this car to idle. At this point it is running well on the road even at 1200 RPM at load. But at idle the car sound rough.
I have tried to adjust the Air/fuel mixture screw without any luck. It just seems like it is not responding or if it is, not by much. I have taken apart the carb and cleaned out all the jets without any luck.

I have checked for vacuum leaks all around the carb. All of the ports have plugs on them except the middle one on the carb spacer, I have that hooked to the dizzy.

Can anyone think of why I wouldn't get any response from the air fuel mixture? I have sprayed carb cleaner around the carb. That did catch one leak but not enough to make the difference to idle.
Anything on the ignition I should check? I put new spark plugs in already.

Before I get any criticism on stripping the carb, I received the carb in a box

There could still be some passages in the throttle body which the carb bolts to. Jeff20B described
some interesting issues with those on his icy build thread. Seems the passages are very small
and easily clog. They are also very precise to cleaning them should be done carefully and not
using just any metal wire at hand. One errant scratch can change the idle behavior.

I would say pull the carb and take the throttle body off and soak and hit it with compressed
air on all the passages. You may be surprised by some gunk coming out of it.

Thank you for your reply.

I have took the carb apart already but I will look at the throttle plates again to make sure I didn't miss anything.

I took it out for a drive and it seems to be lean all over the RPM range if that helps narrowing down someplace on the carb. I thought I had a leak somewhere other than the carb but I have stripped down the intake manifold (no leaks) checked the brake booster thinking that there was a leak there (no leaks), brand new intake gasket (assuming no leaks). It has to be something with the carb. The engine is getting fuel but not enough fuel.

The other thought was that I added an RB exhaust header and removed the cats. So by improving exhaust flow am I going to have to rejet the carb?

Also does the mixture screw adjust the mixture just at idle or all over the RPM range?

Thank you

Don't know if this helps. I am working on a 85 GSL-SE that hasn't been running for several years. Got it running but can't get to idle or run for very long. I drained the fuel tank and put fresh fuel in it when we started to work on it. Ended up pulling the fuel tank off and to my surprise the pick- up tube had a filter basket on it. It was totally trashed along with the tank being full of rust. I looked around and the filter basket is no longer being made. I had to order a new fuel tank and I am replacing all the rubber fuel lines. Hope your problem is easier to fix.

I think it is. The fuel tank was cleaned out before I got it so I didn't have to worry about rust. The carb had white residue from what I am assuming is from the ethanol blend

I think something is plugged. I am going to see if I can source a cuttaway picture of the carb so I can study it better to figure out which part is plugged

Question, does the Mixture screw control the richness of the whole RPM and Load or just the idle circuit?

Solution!
 

Foxed.ca - Mazda RX-7 Manuals

I fixed the issue. It runs SO much better. It is a whole different car.

I was pointed to the RX-7 manual site and there is a great book just for the Nikki Carb. I took the time and read through the theory portion. After studing what makes the idle circuit work, the carb was taken apart, ever part checked and sure enough the fuel inlet on the slow jet was plugged on the bottom. Both of them were plugged.

Cleaned, reassembled, put back on and started to idle at 1000 right away, after some tweeking of the Mixture and the idle screw it is down to 800rpm and happy.

It now feels like the secondaries are not kicking in but that just might be the nature of the car also...

When depressing the gas pedal you reach a point when you hit the springs on the secondaries. You should be able to feel the extra resistance on your foot.
If you are in high gear at a low rpm you may not get the full effect. Try 2nd at 3000, then push it past the resistance.
I was cleaning the carb with carb cleaner while running. Always seem to leave some in the secondaries. So I took it out on the main street, no traffic, 2nd gear and punched it. If there had been a back seat I would have been in it.
Mine is an all stock engine and carb.
I use it as a daily driver when the roads are dry and free of salt (Ohio). Commute to work is 35-40-45mph limits. I like to keep it between 3000-5500 rpm and never go beyond 3rd gear. The rpm range gets me the torque for traffic.
You may also notice a flat spot in heavy acceleration somewhere around 2200-2500 rpm. Another reason I keep it above 3000 in traffic. (And then again there is always the fun factor.)
On the freeway and cruising, I go up to 5th.

I don't get that punch back in the seats while flooring it above 3000 rpm, in fact the car seems to struggle to get to the upper RPMs. Like it takes effort to get it to redline.
However it is not running out of fuel like it is going lean. That would give different symptoms. It could be that timing is being pulled

I really don't want to switch to mechanical secondaries. Rather keep it vacuum and keep it simple.

Besides setting up a go pro, is there a way to tell if they are opening?

You can hear it. Its an extremely audible thing.

Start car, remove air cleaner. From the passenger side reach your left hand down and grab the throttle shaft. Open the throttle about 1/2 way. You'll see a good spray of fuel in your primaries. Holding that, snap the throttle quickly all the way open a couple times. You should see some movement of the secondary throttle and some fuel as well. It's pretty loud.