I've been having the same problem for about 5 months. Bike runs fine going down road until it gets to normal operating temperature then starts lunging and backfiring really bad. If I get it to about 80mph or under 50mph it runs fine. Bike has had the ears taken off and have k&n filters. I also have the silly vacuum petcock open so it's not that. I thought maybe something wrong with carbs but have completely dissasembled and cleaned after this problem, didn't help. Vacuum hoses not kinked. Fuel flows fine out of tank when disconnected, Float level checked, But ran fine for miles and float bowls shouldn't just move anyways, clinked air filter, ran seafoam twice before cleaning carbs, double trippled and quadruple checked carb intake hose and seems tight and solid, vent hoses are not kinked but I sprayed some carb cleaner in through where the vent hose goes just incase something built a home there.

I just don't think it has anything to do with the fuel or air system. Any ideas on anything in the ignition system that could be causing this? I would think that it would be doing it from a start unless it gets warm and starts acting up maybe in the ignitor? But then at high rpm it goes away and don't seem to notice under no load, if I pull in the clutch and rev it doesn't do it.

I'm outa ideas gonna go look at the price of harleys now

did you rejet the carbs after you took the ears off?

lance your thoughts?

yep I got the kit from pro jet or somethin like that. But bike ran for about a year just fine after I took the ears off.

Does your tach bounce around? If so, check you battery terminals, they might be loose.

^X2 there have been several members complain of the same problem you speak of and it has usually turned out to be the battery cables and be sure to check your battery ground to frame and the engine ground at the back of the engine and transmission case.

i've removed and cleaned them. I've never checked the battery voltage after I'm having problem though. My tach doesn't jump up and down it acts normal.

How old is the battery, and are you charging the battery between runs? Battery could not be holding a good charge and after a short while the battery gets low and then not enough power to run the bike and is your charging system working right? Try getting the battery load tested.

I'll check that I guess these bikes are sensitive to low voltage. But battery is not very old and it's a sealed maintence free battery swapped it out probably a month atleast before problems began because I left my lights on. Bike starts up fine though and haven't had to charge it between runs.