Maybe your gas line is dirty? new filter?
rev it high rpm, and clean the carb with carb cleaner... try not to get much of the carb cleaner down the carb.
if it's auto-trans, check the fluid level, mine did that with low fluid.
check your idle screw for gunk on the end... don't loose the spring
new air filter?
what kind of dizzy is it? is the vacuum cannister still working? (try blowing, if you suck you might get a lung full of fumes)
at high rpm and HIGH temp, drizzle 1 bottle of distilled water (12-16oz) down the carb hole. SLOWLY, should take 60-90 sec's per bottle if you do it multiple times.. this will clean and not harm your cyl walls, valve area's, exhaust ports, piston head, cleans anything that the water comes in contact with that's hot. I've found this to help alot with dirty oiled engines.
just some things to think about.
Richard