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Rough Idle And Running When Cold Fine When Warm


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1974 with Weber 32/36 5 speed.

Have had the car for several years, always started great when cold and ran great, including a 3,000 mile trip last summer.

Now runs very rough(bad misfire) when cold.

If not on high idle will stall.

If trying to drive it, it must be kept at about 3,000 rpms or more to not misfire and buck hard like a horse. #whiplash

Need to stay in 3rd gear at about 35+ mph to be drivable.

Once warm runs well and can chug around in 4th gear at 25 mph with no misfire and bucking.


Choke seems to be set right.

Plugs are good.

New plug wires(especially after noticing one touching a coil lead and showing some arching residue)

New fuel filter, fuel pump and lines under the hood(lots of fuel in filter, more then before pump change).

Checked for vacuum leaks at carb base and intake to head with stethoscope, could not hear any.


Any thoughts on what to check next?

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When was the last time the timing was checked? Have you checked for any leaks in the carb itself? Spray carb cleaner all over the car and the intake. see if the idle changes….to me it sounds like there is some leak somewhere until it warms up and the leak seals itself. Have you checked the coolant and oil? Head gasket? Maybe a slight leak allowing coolant into the combustion chamber when cold, seals when it warms up?

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Are you sure the choke is behaving?  Is it the OEM Solex with it's problematic automatic choke (fast idle cam wears out so it won't fast idle while the choke is on).  Or do you have a Weber, and if so is it a manual, automatic water or electric choke?


Have you "set" the choke when the engine is cold by flooring the accelerator once or twice, and then pulled the air cleaner to verify the choke plates are fully closed?  Or if it's a manual choke, pulled the choke knob all the way out and then checked for closed choke plates?


Sure sounds like a choke problem to me...



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