My car acts like it’s flooded...but I’ve made the obvious fixes
I have a 1968 Mustang with a 289 V-8 and a Motorcraft 2-barrel carburetor. It appears to be a later model 2150 carburetor rather than the original type model 2100, but they are similar.
My problem occurs when trying to restart the car hot after it has been sitting for a while. In these circumstances it acts as though it’s flooded.
Having had similar issues with another car I verified that after stopping the engine hot, fuel continued to leak into the carburetor throat.
I rebuilt the carburetor with a new float, needle, and seat, setting the dry float level and verifying the proper wet fuel level in the bowl with the car running at idle. I set the pump rod stroke and bowl vent adjustments per specification and verified the bowl vent is open with the throttle closed.
The carburetor still lets fuel in after stopping the engine when it’s hot. It seems to take a few minutes of soaking up engine heat after stopping and then fuel almost gushes into the throat until it seems the pressure is relieved or until it runs out of fuel to leak.
Common causes of the problem you are experiencing include an incorrectly adjusted float, clogged bowl vent, or something that prevents the needle from fully engaging and sealing against its seat, such as a bent needle or contamination on the seat.
You seem to have eliminated these possible causes so I suggest next looking at anything that may contribute to heating up the fuel in the carburetor or fuel line. If the fuel gets hot enough it will expand and build up pressure that is sufficient to move the needle off its seat and cause fuel to run into the engine and flood it.
Assuming your engine is equipped with one or both, if the heat riser tube that runs from the exhaust manifold to the air cleaner or the heat riser valve between the engine pipe and exhaust manifold is stuck open it will add unwanted heat to the fuel system. Carbon deposits stuck to the underside of the intake manifold also can help heat up the carburetor.
Is the fuel line running to the fuel pump or between the pump and carburetor against or very close to an exhaust manifold, the water pump, a radiator hose, or some other source of intense heat? Is the fuel line running from the tank to the pump touching or close to part of the exhaust system?
You can try adding a heat insulator between the carburetor and intake manifold if the car doesn’t already have one. You also can wrap the fuel lines with insulation designed for that purpose. Such insulation is readily available from some auto parts stores and many speed shops and race parts suppliers.
Another thing to take into consideration is the engine’s typical operating temperature. If the engine is operating much hotter than it should then, of course, the fuel in the lines and carburetor will be that much closer to its boiling point. Check the engine operating temperature and if it’s too hot figure out why and do what’s necessary to bring it into a normal temperature range.