Trouble with warm start

[RobTav63]

Last Saturday, I started my truck, walked the dog while it warmed up, and then stopped at the deli down the road for a BEC. Since the truck was already warmed up, I killed the ignition. Got out of the deli 5min later and it had a hard time starting. Cranked fine, but wouldn't turn over. After a few tries, I was able to start it by flooring the gas and cranking the starter. Even after it "started", I had to keep the pedal floored to keep it from stalling out for about 10-15 seconds, then it reved up and ran fine. Had no issues for a couple of days, but then the same thing happened this AM - killed the engine while I ran into the deli (after 10m of driving) and had to start it the same way. No issues starting cold. It's an 83K5, edelbrock 350 with a Q-jet. I'm going to try to replicate the circumstances and be very conciencious about what i'm doing with the pedal, and take some notes. Anyone have any ideas on specific things I should be looking for? I've searched the forums a bit, from what I've read, I suspect maybe vapor lock. What are some different approaches to diagnosing?

 

[RobTav63]

some more info: I always cold start with 2 pumps, turning the key with the second. I usually don't do anything with the pedal when warm starting (but may have w/o thinking I these cases). Also worth mentioning, my oil pressure sender for the choke was leaking about a year ago. I pulled it and capped the line. Other than the dummy light, i've had no issues until now. The carb is CA smog compliant.

 

[blazer74]

Flooding within 5-10minutes of shutdown.
Several possibilities.

Float saturated and heavy.

Needle/ seat worn, or debree.

Fuel pressure building up due to heat soak overcoming needle/ seat and flooding.

Too much fuel pressure, have you changed the pump recently?

Some aftermarket pumps can cause the prévious 2 by too much pressure.

choke coil going bad.

I'd check fuel press and fuel filter.

It's only happened twice so not much to go on tho.

 

[diesel4me]

Leaky well plugs maybe,seeing its a Q-jet..the fuel in the bowl oozes out into the intake and creates a very rich mixture,which can foul plugs or make starting difficult..

Some engines with Q-jets suffered from easily fouled spark plugs--if the choke pull off failed or wasn't opening the choke butterfly wide enough after a cold start,often the engine would just chug=chug-chug and load up badly,and once it stalled,the plugs would refuse to fire up again,and you were lucky to get it to start using the "hold it to the floor and crank" method--usually all 8 plugs had to be tossed and replaced to get it running again...

If you choke pull off isn't working or isn't opening the choke enough when it is warm,it'll flood it easier..

The '75's were the worst year for doing this,when they first came with HEI,and they put in extra wide gap plugs using an .080 gap...it proved too much for the stock coil under cold weather starting,and it led to easily flooded engines..the next year GM revised the ignition to use a .045 gap plug instead...

Heat soak can occour when a carb gets too hot from heat transfered by the intake to the carb's base too--Q-jets came factory with a thick base gasket about 3/8" thick to insulate it better from the manifold,to prevent vapor lock and fuel from boiling in the carb bowl...adding a thicker gasket may help if yours is only using a thin one..

 

[RobTav63]

thanks for all of the info guys. It still has the stock mech fuel pump, so I doubt that's the culprit. I have had problems with short plug life, so i'm suspecting the well plugs. It would explain why "flooring the pedal" worked both times, sincr that would lean out the mixture (right?). I'm going to get into this weekend, and post my findings.

 

[blazer74]

thanks for all of the info guys. It still has the stock mech fuel pump, so I doubt that's the culprit. I have had problems with short plug life, so i'm suspecting the well plugs. It would explain why "flooring the pedal" worked both times, sincr that would lean out the mixture (right?). I'm going to get into this weekend, and post my findings.

Well plugs can certainly cause this, should also be loosing fuel in the bowl and make cold starting longer if the truck sits any amount of time. If it's a daily driver you may not notice it.