Occasional stall at stops. Otherwise smooth as butter.

[Serpico]

1976 Spider 124 49k miles with an ADFA carb. The car is set to ~1000 RPM idle and runs smooth and perfectly 99% of the time. However, every once in a while as I am coming to a stop the REVS will just drop hard as I clutch in and the car stalls. It starts IMMEDIATELY and usually runs perfectly afterwards (sometimes it stalls again but stays running smoothly after the second start attempt). During the stalling I can keep the car running if I touch the gas pedal lightly and bring the revs up to 1000-1500.

Prior to the stall there is no power loss, no sputter, nada: it runs perfectly until this occasional stall.

The fuel system is 100% new from the tank all the way up to the carb. New coil, plugs, wires and timing is spot on. Fuel filters are clean. Plenty of fuel and spark. Emissions have all been removed and ports plugged (long before this started happening).

My suspicion is: You know when you REV the car and then let off hard; and the revs drop to around 1500 fast THEN level out slowly? Well that "leveling out slowly" isn't happening causing the stall. What is responsible for that "leveling out"?

Any suggestions greatly appreciated! Thanks!

[18Fiatsandcounting]

An important question: Does the engine stall when you let off the gas and put the clutch in, while still coasting? Or does it stall when you put the clutch in and start braking?

If the former, then one possibility is that the remnants of the fast idle system (an emission device) are somewhat active, and it's opening up the intake manifold to additional air which leans out the engine resulting in a stall. If the later, then one possibility is that your float level is set too low. The braking action moves the fuel in the carb bowl away from the jets, and the mixture can lean out, again causing a stall or a least a faltering in the idle.

Another possibility is that your idle is just very weak, so try backing out the idle mixture screw a half turn.

A very remote possibility is that you have a lightened flywheel, and that loss of rotational momentum can cause idle issues if the idle is on the weak side.

-Bryan

[Serpico]

Thanks for the response sir. I will try those combinations and report back as I really don't clearly recall. I would say (recalling the situations) that is happens when both brake and clutch are fully depressed. But the stall is not consistently happening - very random as it seems.

The only connections to the carb are fuel line, fuel return line, idle solenoid, linkage and water lines to the choke. All else is capped.

That being said - I started down the remediation road at the solenoid: It cycles when power is applied, and it was clean (I removed it). HOWEVER it was "loose"; backed out about 1/4 turn which may lead to poor grounding. Also, since I do not know where the solenoid power is sourcing from at this point (since the emissions and tachymetric switches have all be removed): I ran a new ignition ON power line to it.

I drove it this morning for about 20 mins with no issue... the real test is when I am in traffic lol - that's when it seems to test my grit.