rough when engine warm

[fiveseven]

I have a recent new rebuilt 390. The engine starts fine when cold but as soon as it gets to operating temp it runs rough and wants to die. Ive had a holley and an Edlebrock carb with same results. Does any one have  any ideals.

[Diogenes]

There are so many variables here, so many possibilities. It is so difficult to diagnose things this way (I've recently been on this site looking for ideas myself), moreso with a lack of detail.

What engine?
What type of valvetrain? Adjustable or non-adjustable? OEM or aftermarket?
If adjustable, have you checked valve adjustment?
If non-adjustable, are the pushrods correct length?

It could be so many things, this is just what popped into mind.

[jayb]

Did the carbs you tried have an automatic choke?  Is the choke not opening fully?

[Riderjeff]

Since you say the engine acts the same with both carbs, let’s assume they’re not the issue.  If it “starts fine when cold”, when the mixture is rich, and then doesn’t want to run when warm, perhaps you have a small vacuum leak that’s leaning it out.  Use some starter fluid with a tube on it and try spraying specific spots.  Check your vacuum hoses and connections as well.  If you have a leak the engine should rev up some when the starter fluid is sucked in.

[fiveseven]

The engine is a 390, just rebuilt by a good machine shop. Pretty much stock. RV cam, It ran good for a couple of weeks then got a petronix ignitor 3 dist. I installed another carb dist and coil. But the same results. When engine is operating temp it will die or try to.

[Heo]

Is it while standing still idling or running down the road with some rpm it dies? Hot weather right now?

[1964Fastback]

I would try to verify "operating temperature", either with a tested gauge and sender or maybe an IR thermometer if you don't have a gauge.  New builds sometimes are tight and overheat.

Have you gone over the basics - radiator full of 50/50 water and antifreeze, oil level is okay and dipstick doesn't look like chocolate shake (water in oil)?  Maybe the thermostat is stuck shut?  As mentioned, could be a lot of things.  Do the plugs look okay?  If it does it while idling, you might try putting some cold wet wash cloths on the fuel bowls in case it is percolating.  Or just see if you can see fuel dripping in the carb barrels.  Careful sticking your head over it to look - maybe use a mirror.

Pat

[428Marauder]

Do you know that you have your timing dialed in? Have you tried adjusting it all?

[fiveseven]

After several days I think I have come up with good fix. I installed a 12 volt wire to the coil using a relay. Pentronix recommends this. I also ramped up the initial timing to 18. I have driven it and am convinced this will do the trick. Im still gonna play with the timing to find the sweet spot. I appreciate the advise.