After driving my car for a while it is sometimes difficult to start (have to turn it over for 3 or 4 seconds) and when it does start there is a strong odor of gas. I also notice that when it is warmed up it stumbles a bit at idle. Every four or five seconds it will shudder and the idle will decrease. It never dies and drives like a champ. The engine is a 283 with a Rochester 2 barrel. I adjusted the two mixture screws by backing them out 1 1/2 turns like my shop manual says. Timing is pretty advanced (timing mark flashes at about 12 oclock) and I am running a petronix ignition kit. Any help? Might be a simple idle issue?

Might check your float level:
http://www.tocmp.com/manuals/Carbs/Rochester/2-Jet/Manual/index.html

Could it be the fuel is percolating in the fuel bowl from the heat of the engine transfering though the mainifold?