1983 GSL; 12A stock (no cat, Monza header/exhaust). Running the stock OMP with Premix (1 oz/gallon) as backup.

I've been having an idle problem since I got the car 1.5 months ago. The idle has been between 1100-1200 RPM. Vacuum leaks seem unlikely; I have replaced all tubing on the rats nest *except* the crankcase circuit (probably doing that today).

This is not the reason I'm posting but gives the background. The reason follows.

In fiddling with the mixture screw, I could get the idle to 800 but with heavy hunting. Adjusting the idle up is the only way to keep the hunting to an acceptable level. In doing this, I've been smelling more and more of that lovely burning carbon coming from the engine.

In fiddling with this, I have created a new problem that I suspect is air starvation.

The car will rev to redline in first and second gear. If I shift into third, it stops firing properly but does not seem to flood. Once stopped, the engine will restart and rev again in 1st and 2nd gear as described above.

To me, this seems like an airflow issue. Because of the carbon puffs off and on, I want to be sure of my approach before I go into it. So I'm asking for input because I don't want to break something while trying to fix it.

My plan is:

(1) Reset the Nikki; tighten mixture all the way in and then 3 turns out and adjust idle down.
(2) Run seafoam in the gas at the next fillup.

Thoughts? Things to check for? Ideas? Suggestions?

 

fuel filter>? Vacuum leaks and a shitty port job on a RB intake did that to me.

 

Hmm. Well, I've pretty much ruled out the vacuum leaks and the exhaust has been fine for a while.

Yeah, maybe fuel filter, but I'd expect fuel filter issues to show up in 1st and 2nd gear as well - and RPM range is fine until 3rd gear which leads me to believe air. Fuel filter will be changed anyway - but the issue only really showed up when I was playing with the carb.

 

fuel delivery problems will show up with load, which is higher in the upper gears, so your symptom could be a fuel filter.

for the idle problem, i would set the idle mixture to what the shop manual says (Foxed.ca), i think 2.5 turns out. then adjust the idle speed. most cars are happy @the factory mixture setting +/- less than 1 turn, so somewhere between 3.5 turns and 1.5 turns.

 

I guess that depends on the gear ratio. Not trying to be argumentative, just saying I see your point.

Yeah. I think I'll be doing that tomorrow; I drove the car today and tested a slow 3rd to 4000 and started the bog but saved it. This ruled out the air starvation theory I had since I wasn't doing it as fast (pedal down, acceleration) and was moving at a slower speed.

Whistling in the exhaust (no cat) has me also wondering how much carbon I have in there... time for a 20 mile high RPM run after I do the fuel filter. Will update this when I have solved it; may be up until Saturday depending on NonRotor Factors.

 

What you have describes is the classic symptom of a clogged fuel filter. The filter will flow just enough to get you to 3rd gear at wide open, but just can't keep up after that. Don't argue, just consider yourself lucky that you'll get away with only $3.00 in parts and a half hour of your time.

Stock filters, even when brand new, can barely flow enough fuel to satisfy your rotary. To ensure I would get adequate flow for more than a year, I ran two filters in parallel so that each filter only has to work at 50%. I did that about 3 or 4 years ago, and haven't had to swap filters since. Before that, it was a yearly task that had to be performed. There is a thread in the Archives section showing details on this mod.

Good luck...



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The stock filter flows fine after you replace the barely adequate when new fuel pump.

In my SA, with the stock pump, a fuel filter would start to give me the 3rd gear or 80mph stumbles after 3000-5000mi. Holley pump, and I could go forever on a filter.

I never ran a stock pump after that. First thing to go when acquiring another RX-7 was the fuel pump.

 

I was considering a parallel setup...

 

Considering the fuel pump is stock and close to 30 years old, this also seems like good advice. First step, the filter. Next step, fuel pump. Gotcha.

 

Took 20 minutes and popped in the new fuel filter. Took it on a run immediately afterward: symptoms gone.

Opened fuel filter: rusty mucky stuff.

Of course, I run the tank as low as I can before I fill up - typically takes between 12-13 gallons - so I expect that filter to get nasty again, fast. Figure I'll have to change it one more time this year.

Thanks to you folks, I wasn't off chasing gremlins. Greatly appreciated!

(Also happy to say I have the original jack, etc.)

Lesson learned. Thanks all.

As far as the stock fuel pump - is it really that restrictive? It seems to be doing OK with me, though I'm not at the track with this daily driver...

 

The stock pump, with a fresh filter, seemed capable of keeping up with my Sterling carb once I did the dual filter setup. Swapped to a Carter pump after a year to be on the safe side, but saw no additional performance boost.


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I think before the end of the year I'll figure out how to do a dual filter setup that isn't restrictive. Given the history of the car, I expect more muck:

The 2nd owner bought it after it had been sitting for about 5 years. It wouldn't start. He pumped out the gas, changed the filter and refilled. It ran. Based on the muck I saw, I expect a few changes and will drive it hard on low gas to try to suck the gunk into the filter.

How did you go about the dual filtert? Y connector? It's an appealing idea and one that I might prefer doing sooner than later.

 

Here are my instructions on the parallel filters (along with a lot of other suggestions by supporting members): https://www.rx7club.com/1st-generati...er-mod-528445/

 

Nicely done. Most importantly, easy to maintain.

 

Thank you. It has been working great for me so far.

 

I just replaced the fuel pump and filter on the '80 with a Summit Racing setup and put the fuel pressure regulator under the hood where it belongs. It's much cleaner under the car now too, instead of that mess of fuel lines running back and forth I just have the tank line to the filter, then from the filter to the pump, then from the pump to the front of the car.

You'll see what I mean when you get under there