Note: as always, we’re assuming the engine is properly tuned and will only cover issues with the carburetor
The most common cause is the choke unloader or reloader being set improperly
- automatic choke improperly adjusted or damaged
- fast-idle speed incorrectly set
- accelerator pump stroke out of adjustment
- air cleaner hold-down nut too tight, binding choke plate
- carburetor to intake manifold nuts loose
- intake manifold to cylinder head mounting nuts loose
Could be caused by the Thermostatic Valve equipped on some vehicles.
As the valve opens, it allows outside air to flow directly into the intake manifold, leaning out the rich air fuel mixture. Valve starts to open when engine compartment temperature reaches 140 F, or 60 C and fully opens at 167 F, 75C.