Engine won't start once warmed up.

[pkorpi]

Hi everyone, I recently purchased a '72 Challenger from Michigan with a 340. It was not running once I bought it. Since then I have got it running, here is a list of what I've done to get it running decent.

new rebuilt carb
new air intake
new plugs and wires and rotor
new ignition module
new battery and alternator
new mechanical fuel pump and rubber hoses
new fuel filter

Now the car will fire up and run with a rough idle for about 20-30 minutes. If I shut the car off after this time it will not start for at least an hour....is it the typical vapor locking issue that i'm having? I read some threads saying possibly the fuel pump pushrod? It's been doing this for about 2 weeks now and I'm lost on what to try next. Should I just throw an electric fuel pump near the tank? Any suggestions would be great!

Thanks in advance.

I'm kind of a newb so try to explain as best as possible 

[Bullitt-]

Sounds like the problem is heat related, two common issues to do with heat are the ignition coil or the pickup in the distributor.   
Fuel push rod is not found on small block, could be vapor lock, just leave the fuel cap off to find out. 

[cudabob496]

if ecm is near exhaust, it can get hot and prevent starting
make sure the engine has good ground straps.
protect electrical components from heat.
I would not have considered vapor lock initially, unless really hot out!,
assuming your engine is running cool.

Read this, and you'll be an expert:

http://www.moparaction.com/Tech/archive/roadside.html

[Chryco Psycho]

firstly determine if you are getting spark when you are cranking the engine once it is warmed up , sounds like you are if the engine will stay running until you shut if off . next you need to look down the carb & see if the fuel is boiling over into the  engine from the heat , my guess is it has something to do with the carb settings , you do not say what type of rebuilt carb you are using

[74 challenge]

I have gas boiling issues I can usualy get the car started by pumping the pedal 3 or 4 times before turning the key. That being said I need to leave the car for a few minutes before this becomes an issue. If I were to hit the ignition immediatelly after shutting it down it starts right away.

[pkorpi]

I have gas boiling issues I can usualy get the car started by pumping the pedal 3 or 4 times before turning the key. That being said I need to leave the car for a few minutes before this becomes an issue. If I were to hit the ignition immediatelly after shutting it down it starts right away.

Yeah that is exactly what mine will do too. As long as I don't wait more than a minute or so to start it will fire right up...

[pkorpi]

firstly determine if you are getting spark when you are cranking the engine once it is warmed up , sounds like you are if the engine will stay running until you shut if off . next you need to look down the carb & see if the fuel is boiling over into the  engine from the heat , my guess is it has something to do with the carb settings , you do not say what type of rebuilt carb you are using

Yeah the engine will run all day just have the starting back up issue which makes it difficult to run errands and things like that.

It's an Edelbrock 1406. I got it from a carb rebuild shop so I'm assuming that they rebuilt it just fine. The only settings I have played with are the air/fuel mixture screws and the idle screw. I'm at a high elevation (anywhere between 6,000-8,000ft depending where im driving) so do you think I should jet it a little differently to accommodate? I'm not exactly sure what size is in there at the moment, probably just the standard size.

[pkorpi]

if ecm is near exhaust, it can get hot and prevent starting
make sure the engine has good ground straps.
protect electrical components from heat.
I would not have considered vapor lock initially, unless really hot out!,
assuming your engine is running cool.

Read this, and you'll be an expert:

http://www.moparaction.com/Tech/archive/roadside.html

ECM is on the firewall so not getting too much heat. I'll double check all the electrical components. Thanks for the website, it had some great info!

[Chryco Psycho]

too much heat under the carb , if you have room add an insulating spacer , you could pull the intake & block the heat crossover , it would make a big difference . If the carb was shipped to you the float level could be off also .

[pkorpi]

Thanks for the info everyone. I ordered a spacer and fuel pressure regulator. What pressure should I set the regulator at? I've seen anywhere between 4.5-7 psi.

I'll put them on within the next week and see how things change.

[Chryco Psycho]

5.5 PSI pressure is not as critical as volume 

[jimynick]

One other thing to consider is heat soaking of the starter. If you can lay your hands on an old fashioned induction guage, see what kind of amperage is going down the positive cable when you crank it, hot. Just a thought. 

[cudabob496]

One other thing to consider is heat soaking of the starter. If you can lay your hands on an old fashioned induction guage, see what kind of amperage is going down the positive cable when you crank it, hot. Just a thought. 

Another good reason for hefty engine grounds, and a starter heat shield.

[KingCuda440]

I would check the ignition timing to make sure it is not too high.  Rule that out first.

[Kapteenikosmos]

Yeah that is exactly what mine will do too. As long as I don't wait more than a minute or so to start it will fire right up...

Sounds like the carb is just boiling and dumping gas into cylinders after you have shut down the engine. My cars tend to do this quite often, sometimes in a cold weather too. Insulating spacer under the carb helps alot and also the heat cross over channels could be blocked from the intake.

Have you tried the "standard" practise for starting up warm flooded engine? Mine starts the best when I depress the pedal (only once!) about 50% and keep it there while starting the engine. It usually takes about 10 seconds of starting to clear up the flooded condition and then the engine roars back to life.

On my Challenger and especially in the Fury I can easily smell when the gas starts to boil in the carb and it starts to drip into the intake manifold. This usually happens few minutes after the engine has been turned off.