hey i am new to the forum and i would like to ask you guys to help me out a little . i have a 80 ford f350 and when i hold the rpm to about 1200 rpm it has a reall rought hesitation and it runs real bad. then while its at 1200 i will put my hand over the intake on the carb and the idle will rise up and get real smooth. i was told this could be a vaccum leak but i am not sure. i really hope you guys could help me out in getting this thing back on the road. thanks alot.

 

Sounds like a vacuum leak to me. try spraying some penetrating oil around the manifold & carb & see if the idle smooths out. Don't use WD 40 it is flammable so it would be like spraying starter fluid. Carb cleaner will work also.

 

You could also have a piece of dirt clogging one of the main jets in the bottom of the carb.

 

Sounds like a vacuum leak between the carb and the manifold. Check to see if you have loose bolts/nuts that hold the carb down. If they are loose, and have been that way awhile, the gasket may be deteriorated.