My car was running fine, and something changed and now it can't decide if it wants to run fine or not. I can cold start it, and the engine usually runs ok, and will idle all right for a bit, but then the idle will start sagging slowly. The engine runs perfectly at wide open throttle, and if the idle is getting bad, it will often seem to come back to normal after a short run at WOT to 60mph. It will inevitably start sagging again, though, and after a while, sometimes 15 minutes, sometimes more like half an hour, it'll get really bad, like 100rpm, and trying to rev it doesn't help and it just dies. If the engine is hot, it will not start. I'm pretty sure it's not overheating, the temp guage reports within the normal range. The engine cranks but refuses to fire.

So to summarize, my car is experiencing an intermittent, very rough idle which will cause it to die, and a complete failure to start warm. Performance at WOT is normal. I'm thinking maybe the carb? Something wrong with the idle circuit perhaps.

Now the car:
1981 GSL
12A motor stockported, built by Marvelspeed 6,000 miles ago.
Dellorto DHLA48 carb
no cats but stock manifold and muffler.
recently replaced plugs, plug wires, battery cables
The ignition and fuel systems are all stock

 

Hot start issues... maybe you flooded the motor... I just had that last weekend. Take out the spark plugs to see if they're wet, if they are then the engine is flooded and clean them with engine decreaser and brake cleaners. Use wire brush to clean the tips as well. Check the carb, you will a sight glass on the side... look from the radiator and you will see one and there's another one at the opposite side, unscrew the screws under it and drain them out. Put the spark plugs after it dries, then turn the key to on and the fuel pump will pump fuel and the sight glass on the carb will go up to half way, normally. Then start the car, have someone to look at the sight glass when you have the key on ON. If that's not the case, then I don't know whats the deal. Hope this would work.

 

I don't think it's a flooding issue, because it invariably starts up just fine when it's cooled down. Cold starts are no problem, it's starting it when the engine is at operating temperature that fails.

 

This might seem like a dumb question, but since you have an aftermarket carb, are you premixing the oil/fuel, or using the stock OMP?

 

Hmm. I see. I am not familiar with that, good luck in searching.

 

Actually, that's not a dumb question, but I am using the stock OMP. Although, for obvious reasons, I do not have a rats nest.

 

https://www.rx7club.com/1st-gen-archive-71/other-end-all-no-start-threads-warning-book-inside-360701/

 

I fixed my idling problem by just shortening the throttle cable (manual says 1-2mm of play and I had nearly an inch or so).

 

Ok, so premixing is not causing the idle mixture to be incorrect, as can occur when mixing too heavily. It sounds like the carb is need of attention.
When the idling issue starts, does it seem to be running too rich or lean? Could be a simple float adjustment, or a jetting issue. What fuel PSI are you running? Some cheaper regulators and gauges are known to be very innaccurate.
I also asked about the oiling, because a buddy had a similar issue, and it turned out his OMP wasn't working correctly. His was not starting after warm. Adding premix helped greatly.

 

Hmm.. check the radiator for bubbly bubbles. My friend had the same prob and turns out he was leaking water into the motor.. told him to give it a break in period but nooooooo...

 

Not familiar with the Dell designations, is the a wrap around side draft, down draft or straight off the intake, pointing to the firewall? I'm guessing a wrap around.

With the heat you have had in TX lately, it could be the fuel in the carb is boiling over after shut down, overflowing and fouling/wetting the plugs.

I would put my money on the carb needing gone through, particularly the pilot circuit. You might try a can of Seafoam in the the take and see if that cleans the carb out, before you tear it down. If the Dells are as simple as the Mikunis, removal, teardown and install is less than a 2 hour job.