Hey guys, First off let me just say i'm new to this site, and hope im in the right place for this question/problem..... Okay let me begin by saying I had this problem since last year, and didnt do anything to fix it until a couple days ago. When i would ride on the highway at about 65-70 mph it would backfire ALOT. What i did was was replace the manifold gaskets, they were pretty bad. Plus since i had the carb off, I inspected it, looked "clean" so i shot some carb cleaner in just because it was apart and maybe would help. And replaced the spark plugs. I took it for a test ride and it was riding great until I got about a block away from my house and it backfired again..... I took it to work today and it was riding pretty good until i went over some train tracks, the secound i went over them it started to backfire again! But "fixed" it's self and was back to normal. I thought it was a little weird that it backfired while going over the tracks. But anyways i took the highway into work today and it backfired once, when it happend i pull off of the the throttle and let it stop. then i got back on it again, and had no problems after that. I dont know if you guys could help with this weird problem or not, but i appreciate the help!!! the set up i have is an S&S air cleaner, Stock CV carb, and a Big Bore kit, when i purchased the Bike i was told that everything was installed by an HD mechanic.