Got a 71 with 454. Engine recently rebuilt, carb rebuilt q jet. Pretty much a stock setup. The problem is the car idles rough after I reach normal operating temp. It's also hard to start back up after parked for awhile. It acts as thought it's flooded. I have checked the float and it is ok. Like I mentioned, the carb is freshly rebuilt. When started from cold, however, the car starts right up and the idle is perfect. Another clue may be that the mixture screws aren't very reactive. Any suggestions?

 

Maybe the float level is too high causing a rich mixture which is OK w/ a cold engine but makes idling and hot restarts problematic.

If it's a foam float and it's not new, then get a new one. Get a brass one if you can find one. The foam floats were notorious for soaking up gas and not floating as well. So even if the float level was set correctly, it would react as if it was set too high.

 

Float is brand new foam. I seems to be set correctly. I did disconnect the vacuum t attached to the the pcv that leads to the vacuum reserve. Now the pcv goes direct to carb with nothing else attached. This seem to have helped with the idle when hot. Vacuum leak in reserve tank? Anyway, I still have to push gas pedal all the way in to start when hot. Seems like a flooding condition. Also runs on/ diesels after shut off when hot. Is this vapor lock from high engine temp?

 

Run-on or dieseling is caused by fuel/air going into the combustion chamber w/o any spark but something hot enuf to ignite the mixture such as some carbon or hot plug tip. One fix for this on smog engines was to put a throttle stop solenoid on the carb that allowed the throttle to completely close when the engine is turned off thereby cutting off the fuel/air mixture.

The fact that you have to do a hot start w/ WOT (activates the choke unloader also which I assume isn't req'd since the motor is hot) seems to indicate flooding which could be caused by high float setting, bad needle and seat, and/or carb w/ a leak. Try your friend's carb.