well in the morning when i start my truck the choke comes on, i let it run for a few minutes and let it idle around 1500rpms, i press the accelerator and get the choke to come off, truck idles normal. i drive it about a mile and come to a stop light and it wants to idle at 500rpms. it wants to idle low for the first 8 miles, then when the truck is good and warmed up, it will idle fine at normal idle, i have a new holley carb and i did a complete tune up, the timing, fuel filter, adjusted the mixture screws, float, and choke. i dont hear any vacuum leaks. i have no clue what to check now. any ideas?

 

your choke may be opening to quickly,bob

 

I agree I think your choke may be coming off a bit early. Turn it a couple of ticks yoward rich (should be clockwise) and see if that makes a difference. After making the adjustment drive it for several days before you decide. If it is still not rcih enouhg then try a couple more ticks but continue to adjust it slowly. When it goes too far it will start to load up a bit in the lower RPM's but then smooth out when the choke has fully come off. You want it rich enough (choke closed) to keep it running but not so rich that it loads up. But, it is a compromise no matter what you do so find the best "overall" compromise by making small incremental adjustments.

Good luck,

Mark

 

Been there done that! I bet that you have and open element, chrome type air cleaner. Right?
You need to reinstall the stock one with a functioning hot air inlet( hose from exhaust manifold) . Your carb is icing up. Common on these trucks. I bet it runs good after the themostat opens and the engine compartment heats up.
This is the only way to correct the problem. If the temps stay above 60 degrees and the humidity isn't 100%, then you can run the open element air cleaner.
I learned from experience.
Jimmy