My 1983 Mercruiser 305 with Thunderbolt Ignition has to warm up for about 20 minute before it runs good. I have replaced plugs, wires, cap, and rotor. Cleaned the carburetor and made sure that the choke was working and not sticking. When I start it when it's cold it fires right up and goes up to high idle and will run at high idle for a while and then will drop down and runs nice and smooth. If I try to rev the engine it will bog down sometimes back fire through the carburetor. If I try to leave the dock I can't go much higher than 2,000 RPM or the engine will bog down. After about about 20 minutes or so I can then run the RPMs up and get good performance out of the engine. The plugs I put in were AC MR43 T and I gaped them at .35 I got this information off the tag on the engine. I checked to see if there any wires arcing but I couldn't see any. I would think if it were wire related it would not get better. All the parts I purchased from this site except the plugs. My last thing to check is timing which I will do tomorrow. What did I miss?