starting problems

In my 86 Iroc the 305 was replaced with a 350. The carburator was bad and I replaced it with a new 4-barrel Rodchestor. Now the engine is hard to start when it's cold and hot. I have a feeling it's the timming but i'm not sure if it's the the distributor, chain, or one of the gears. I really don't want to take out the engine are there any other posbile solutions to my problem? :disappoin