Running Great >3000 rpm, runs rough and dies below
 

Hey guys,

I've searched and read many threads but can't quite find the right one. I don't post often as I can usually find the answers hidden in the depths but haven't had that luck this time. If i missed it, I apologize in advance:

The background:
1. 85 GSL, rats nest removed, racing beat header/muffler and thats really it. Otherwise bone stock. Recently (low miles anyways) rebuilt engine.
2. I'd been driving my rx7 for around 3 weeks, brought it out of a 2 year storage (with occasional starting and whatnot) but it had been running great. Top notch.
3. Went over to a buddies, was going to take him for a rip, did the unthinkably embarassing thing and stalled the car. Thought I mighta flooded it becuase it wasn't starting easily as it normally does, so gave it the "shot of sea foam" treatment and started right up. HOWEVER....

The problem:
1. Upon starting after the stall it didnt really want to idle. Anything below 1500-2000 rpm it would die off but I thought ah this cant be a big deal, we'll go for a rip and itll clear things out. It did not.
2. Starts quickly with choke, will 'idle' with choke anywhere between 2k-3k. Once it falls below the 1800 rpm mark, it just wants to die (sounds like running out of fuel)
3. if you "catch it" with the throttle, or choke then it will come back to life around that 2-3k mark.
4. It feels rough between 2000 and 3000 rpm. Just doesn't purr quite as smoothly as it should or did.
5. Above 3000 rpm, it runs great. Purrs great, pulls great. Is fantastic. Partial loading, heavy loading just all round runs well above 3000 rpm.
6. At that 1500-2000 rpm, one of my primaries dribbles more than it sprays/atomizes like I feel it should. That being said, I hadnt observed fuel flows in the primaries before this event.
7. if you use choke or gas you can maintain that above 2000 rpm mark.

I am absolutely stumped. I have checked:
-plugs (look fine)
-coils - checked out
-distributer cap (is fine)
-Fuel filter (replaced)
-fuel pump flow - gives the 1100ish CC in a minute as it should.
- checked for vacuum leaks - couldnt find any (but i could be mistaken). all my lines and plugs check out as well

Am I missing something? Obviously, but what. What is especially stumping is that it was after a single isolated event. It runs well above 3000 rpm but not at all below 2000 and roughly in between the 2.

Can you guys offer any advice?

Thanks,

Jesse:scratch:

Remember everyone checks the fuel flow going into the carb, but don't forget to check the return fuel flow. I may be the only one on this forums who had those screens clog up.

Update:

Great fuel to the carb, solid return from the carb.
Swapped carbs (total of 3 carbs tried) and still no luck. Runs the same across the board which leads me to believe it is not a carb issue.

Could ignitors be an issue here? Coils are both good.

Can you make a video.

have you double checked timing? ...who knows, maybe the little hiccup could have jarred the distributor


just a thought

Let me know if you figure something out. I am having the same issue except mine is more around 1500-2000 RPM and above. It runs amazingly with either my modded Nikki or my Mikuni 2 barrel above 1500-2000 but below just dies. I've checked compression, entire car for vacuum leaks. I have all emissions off, no a/c, strict race car stuff.

Do you have a gasket between the carb and spacer? If you do, remove it and see what ya get.

This sounds like the exact opposite problem I had. Mine ended up being a timing issue. Dizzy was off by a tooth (too far advanced). You very well might be off a tooth the other way (too far retarded).

Quick update:

Ignition
Timing is good.
Coils are good
Spark occurs in the right order and on all 4 spark plugs.

Fuel
Fuel to carb is good.
Fuel return from carb is good.
Have tried 3 different carbs, all have same issue.

Am I back to trying to find an elusive vacuum leak?

Intake manifold gasket? Bad engine ground?

Maybe try removing the two trailing plug wires and see what happens?

since you have your rats nest removed, i assume that the air control valve area is blocked off?

Check static compression / leakdown. You might have a serious compression leak that hides itself at higher RPM

Sorry for the delayed response guys, I work shift work and have been away.

I have discovered the problem! After troubleshooting everything and overthinking everything it did in fact end up being a stupid vacuum leak. I missed it in my troubleshooting as it was under the carb heat sheat near where the air control valve used to be. I have no idea what used to be blocking it off, but it was no longer there!

Thanks for the help. I cant believe after all that troubleshooting it was in fact what many of us suspected earlier on.

No idle between 1k - 2k RPM 3k runs great.
 

Hey everyone,
It seems I have the same issue here with my 85 GSL. It's all bone stock, and was wondering if maybe I could get a little bit more detail on the fix. It would be greatly appreciated!

Thanks,
Mark

My fix took me forever to find but what it ended up being was a MASSIVE vacuum leak. The vacuum hose/plug that was on the underside of the intake manifold had fallen off and resulted in running like shit below 3k RPM.

If your issues seem similar, check all vacuum hoses, plugs, vents etc to ensure they are properly hooked up. I had thought it might be a vacuum issue originally, thought I'd checked my whole vacuum system, replaced a bunch of caps but missed the gaping hole under the carb on the intake manifold.

this might be the same issue I am having now that I put the car on the road. went from bone stock with no good clutch hydraulics, to "while I'm here I might as well " (you know) reading up on the forum and next thing I know I have a stripped Nikki and no rats nest and did a bunch of things at once, and it wont idle at all. will run like a raped ape while on the loud pedal. startups chokeless aren't that bad. will be better once I *BET* I have a compromised ACV blockoff (only 16ga metal, gonna make one from 3/16" that I have in abundance from an impala frame-wrap job. runs smooth but has some nice backfiring on shut throttle coast down.