I have started noticing that after I shut the engine down I see what appears to be a small fuel slick behind my boat. It looks like it is coming form the top of the out drive. The engine is a 1983 Mercruiser 305 with a 2 barrel carburetor. I have put new plugs, rotor, distributor Cap, wires, fuel separator, and fuel filter. I set the timing to 8 BTDC like it says in the tag on the engine. The engine starts and runs great. I will say that it does take a few minutes to warm up if I try to leave the dock to quickly it will not let me because it will not rev about 1500 RPMs but after about 5 minutes or so its fine. I have verified that the choke is working properly and that it is opening fully and not sticking. I have checked for a vacuum leak and couldn't find any. When the boat is running it is smooth and has good power. The WOT is a little low at about 3700 RPMs but I believe that is due to the prop but I'm not worried about that right now. I really hate seeing the fuel entering the water after I shut it off. As I have said before this boat is new to me so I don't have a lot of back ground on it. I did spray clean the carburetor in the spring. When I changed the fuel filer I found a lot of varnish in it. Am I looking at a carburetor rebuild even though it is running well?