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
Other causes
- automatic choke improperly adjusted or damaged
- Accelerator pump stroke should be .31”, or 8mm. Adjust by bending accelerator pump connection link. Measurement is taken at boot end of accelerator lever.
- 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
- main discharge leaking. If at idle or after turning off the engine you see fuel dripping from the main discharge then the main discharge check weight & check ball may be leaking. This will cause the fuel bowl to empty overnight into the intake manifold. Try seating the check ball by tapping lightly on the ball. Test by pressing on the throttle to see if fuel is coming through the discharge, the test at idle.
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.
