I have a 1948 chevy truck with a 350 from a 1972 chevelle in it. It has been sitting for 20 years but I got it running, however I can not get it to idle low enough without dying and it is only making about 6 in of hg of vacuum. Any ideas what could be causing this? I have tried to find a vacuum leak using the carb cleaner method but have not had any success.