My father has had his 2001 FXSTS carb bike for 3 years and has been running great. Starting a few weeks ago (when the weather got colder) his bike started running funny. The carb started coughing and he started noticing some backfire on decel. I changed the plugs (looked good), cleaned the carb, changed his Kuryakyn hypercharger to a Arlen Ness Big Sucker (he noticed a big improvement with this change), adjusted his mixture screw, and idle. I got the carb to stop coughing and it only does it very little. But the backfiring is still there. Could it be the exhaust gaskets? He is running stock headers with Python mufflers.

It is just funny that all of the sudden the bike starting running crappy after 3 years of running smooth. I believe the backfiring through the exhaust was always present he just paid more attention to it when the carb started to cough.

Any help would be great!

 

Also check the intake seals. Known area for a problem. If too much air is getting in it could be leaning it out. They are not too hard to replace and only cost a few bucks.

 

id check exhaust donuts at the head with time they will fail.i had similar problem i installed new ones problem solved

 

Thanks everyone for their responses. Great feedback!

I double checked when I got home last night that when I removed the Hypercharger I cut one of the rubber hoses that T off the vaccum on top of the carb (normally it is one hose that goes into the top of the carb). This hose operated the butterflies on the Hypercharger. This hose is still sucking air into carb and I need to plug it. I will plug it tonight and see if that helps me out some.