Hi all,
I got a sportster 48. When i first bought it it keep hesitate/jerking on low rpm under 3000, and keep backfiring. As some people say say it's mostly tuning problem, so i get fp4 tuner.
Now it still hesitate/jerking when engine is cold. but if it's warm it's ok but still sometimes hesitate and backfire.
Problem keep coming when i start first time when engine is cold, the back cylinder keep going off, until it's warm. then normal. But you can hear the rpm is going up and down quite much. and got poor mileage.
Any help would be helpful, Thanks.

 

It appears you have a 2010 bike but it's always best to give year of bike when stating an issue.

I would be looking for a leak somewhere in the inlet and exhaust systems. I would also look to see if the exhaust has installable baffles if they are loose or damaged in some way.

Check for loose parts. Check for dirty or blocked air filter. Check electrical connections everywhere especially if copper oxide is present. Clean throttle body and IAT.

 

It’s a Sportster, they all do that.

 

... until they have been fettled.