Hot engine, hard start after sitting.

1971 olds 455 v8, edelbrock Performer Intake, C heads, Holley 4160 double pumper mechanical, 750 cfm.

Now the weather is warming up it seems like a hot start after sitting for some time, like 30 minutes, it acts like its flooded and I have to hold the pedal and crank, then rev it for about 20 seconds and it clears up. Gets black smoke then its fine after clearing up.

I've checked for fuel bubbling out or fuel leaking after shutdown, can't find anything.
Is it possible the fuel vaporizes and floods my filter top with vapors from the heat?

I adjusted my 4 corner idle and stuff for the warmer weather and turned my choke off completely, I have yet to test it again.

I wanted to ask if there was something more I could do to help this, however it isn't an issue for me at this time.

 

I'm going to assume it cranks ok. Check the float levels on your carb, they may be too high letting fuel run into the manifold after you shut it off. Do you know what your fuel pressure is?

 

Yah cranks fine, new starter and strong battery.

Float levels are at the bottom edge according to Holley that is where it should be.

Whatever the stock 71 olds 455 pump provides, that is what I have for fuel pressure.

I also did just install a new gas tank because my old one had a leak in the top, the new tank holds pressure and has a new venting cap which seems to be working correctly, now and then I hear it vent.

Could it be possible the tank pressure is pushing fuel into the carb through the pump slowly while the car sits?

The tank sending unit has a vapor tube with emissions canister and stuff for the olds 307 that used to be in the car. That tube is plugged now and the canister is removed.

Forgot to say, hot day cold start is fine, turn of warm/hot and restart warm/hot a few minutes later and its fine on a hot day, sits about 30 minutes or an hour hot and it has this issue where it is overly rich on startup. sits longer and the issue goes away.

 

Mine does the same thing. I don't know the root cause (figured it was scorching underhood temps during 120+ degree summer days) and I just learned to live with it.

 

Now you mention it I do remember some cars, especially ones with the heavier cams, have trouble starting hot/warm at the local shows and such, they are too rich and sometimes they run the battery dead trying to start it.

Maybe its normal. lol

 

My guess is that the fuel percolates in the float bowl after the engine is shut down and that causes flooding, which necessitates holding the throttle wide open during cranking to get the engine to start.

 

Try lowering the float level a hair, gas expands when warm.

 

I'll check the float level again one more time to be sure.

I had a little bit of dieseling (engine run on) today.
I'm going to lean out my idle screws some more later on to see if that improves anything.

 

That's a good idea for alleviating the symptom under discussion, but I actually had to increase the float level since the fuel pump couldn't keep up with the demand at higher RPM and the float bowl would run low causing the engine to fall flat on its face. Many years go I had a Holley high output mechanical fuel pump, but it suffered the classic crack across the pump arm so I reverted to a factory replacement Carter pump and it can't always keep up with demand.

 

Same. Tho i have stock intake manifold. Really hard start when engine is warm.
Last week after driving in my gears for an hour i came back home, and even investigated the case. Took filter-base off, and the fuel was literally boiling on carb, spreading the fumes across the yard. It dont start right away when you turn it off, wait a minute or two and it starts.
I can get it started, but my fiancee wont. Ive also adjusted to live with it. I quess the temp is just too high, when the whole block is heated up and theres no fresh air washing the engine-bays heat off when parked.

 

I put a 1" 4 hole Plastic (phlenolic or some kind of plastic like that, Geez that sounds like a drink haha, I better get to bed!!) carb spacer under my edelbrock 600 and it helped out alot. You may want to give it a try.

Eric