I have a 98 Fatboy. Last year I put on an aftermarket 6 gal tank. I looks great and now it is truly a "Fatboy". A few weeks ago I started developing a problem with gas leaking out of the overflow tube from the carb. I've had the bike in twice to the dealer and they have looked at the carb and said they see no problems. I think it might be a problem in the gas tank and there is pressure building up and fumes are not venting out properly. When I put the new tank on I put on new vented gas caps. A few years back I had the same problem with the stock gas tank and a indy mechanic I know fixed it by drilling very small extra venting holes in the stock gas caps. I never asked what size drill bits he used or how he did it. Does anyone think this is my problem or have any idea what is causing the overflow and how to fix it. Any help would be great.

 

The problem is more than likely the needle and seat in the carb, or a miss-adjusted float. While it is possible that pressure in the tank could cause the problem, it is simple to test...loosen a gas cap...if it is still coming out of the carb...tank venting is not the problem.