Model 1985 RX‑7 GSL, 12A, stock Nikki 4‑barrel. Key Mods • Rats‑nest delete • Mechanical‑secondaries conversion
Have confirmed float level, rebuilt carb, new coils, igniters, rotor, cap
Vac advance confirmed functional
Two Relentless problems:
1: Continuous, rhythmic stumbling / jerking as revs fall through ≈ 2000 rpm. It isn’t one hiccup—it keeps jerking for 5s as I deaccelreate until idle. Revving in neutral and I can hear the stumble and see the engine shake and sputter as it gets back to idle, so driveline ruled out.
When deaccelerating and the car is jerking, the tachometer will bounce a bit (like 100rpm, not much) which I think indicates the engine is sputtering a bit?
2: Tip‑in bog/hitch right after a high‑RPM upshift (e.g. 6 500 → 3 500 rpm). Sometimes the bog is so bad I can feel a jerk. It was never like this and I ran mechancial secondaries for months prior. I confirmed Accelerator pump is functional and rebuilt for good measure. Only happens after an upshift. Slamming on the gas while still in the same gear does not create this issue!

There was a small vaccum leak I detected with carb cleaner after an intake mainfold job I did (Orings were leaking), I retorqued manifold and the vac leak went away.

I confirmed the following:
Ignition timing & advance spot‑on;
Mixture screw work, I can kill the engine at idle by leaning out the mixture enough, however, it DOES NOT affect the stumbling/jerking no matter how much I turn it in any particular direction.
Float height played with—no effect on symptoms.
changed fuel filters, confirmed fuel pressure, all that.

I rebuilt the carb miticilously, mkaing sure to blow compressed air through each passage. Despite this, still have the issue. It really is taking away from the enjoyment of the vehicle.Thanks—this beast is beating me. Any fresh angles are welcome!
- Konrad

 

Whats your exhaust setup?

Also whatever you did last before noticing this is probably where you should focus.

 

That is a good question. I know the exhaust was replaced by the previous owner, the air pump and all that is removed and I believe they are catless.

So the jerking seemed to have stayed the same or even slightly worsened after I rebuilt the carburetor and has gradually gotten worse. The hitching after an upshift however only started a few months ago.

I think the tachometer bouncing inline with the jerking is a good indication that it is likely air fuel and not ignition related right? Since the bouncing indicates brief combustion events? Could it be throttle plate clearances? I never touched those during the rebuild but perhaps they have gotten gradually worse?

I have also been suggested to check ignition grounds? Would that be wise?

Part of me wants to think ignition based on how the idle mixture and float levels have not changed the outcome. However, the tachometer bouncing in sync with the jerks and all the ignition work I have done pushes me towards believing the issue is with the air fuel/carb.


I have verified compression on the engine on each rotor all three faces and they are all close to eachother