My 2005 Sportster 1200XL Custom backfires, and sputters after riding the bike for 20 or 30 minutes. The bike runs perfect while riding, in town or on the highway(lots of power), but once she has heated up pretty good, every stop sign and traffic light is quite embarassing as it backfires and sputters until I get going again, then it runs fine until the next traffic light. While I sit at the lights I try to rev up the engine, and get nothing, then a backfire, sputter, then after an embarrasing take off, it gets better again. When the bike is cold, the idling and starting is not a problem at all.
Some history:
I bought the bike for the wife, it has too much power and height for her. The bike sat most of the time, but I did put fuel stabizer into it. When the backfireing started I took it to the Harley garage, where they changed the air filter, it didn't help. Next, I asked them to clean the carb, float housing, and high speed and idle jets, they did, it did not help either. The bike starts great, runs great, but just the starting off after it has heated up.
More history for trouble shooting:
Bike is carbed, has Stage 1, has Vance and Hines Stagger short shots, was set with this equipment in a town that is 600 feet lower in altitude (in case that makes a difference).
Also installed a slightly quieter baffle in the V&H pipes (in cass that makes a difference).
Gas in tank is fresh high Octane gas.
Looking for any information on fixing this condition which is costing me money and enjoyment in our short Canadian summers!

 

Maybe running lean when you give it the gas to go.
Which makes me think the accelerator enrichment system, the accelerator pump if it has one, is not working right.

Is like when you give it the gas and it just gasps?? Sputters?? Acts like it is not,"taking the gas"? Won't go good?

It is just the oposite, not enough gas getting to the engine at that instant.

If that is what it seems like.

 

At first I thought it was when I accelerated from a stop. But today I twisted the throttle while I was waiting for the light to change, then nothing happened. Then she gasped and backfired, revved up a little, enough to chug through the intersection, then she took off like a bat out of hell!
And you remember from my first post, this only happens after she has warmed right up, in the morning when I leave for work there are no problems, and on the way home just when I get back into town after a couple of traffic lights, she starts acting up!

 

Could be an intake leak. Otherwise I bet it is what I said. Specially what your last post. At the light, quick twist,,,,,Nothing.

No gas there for whatever way it is suppose to be there.

If you got a accelerator pump, something is not right. pump or its check valve.

I know Holleys and such. All the same more or less really.

 

Backfiring out the mufflers or the carb?

 

It is backfiring out the mufflers mostly but the sputtering (or other backfire) may be coming out the carb. When it does its thing I panic about getting stuck in the middle of the intersection and don't pay enough attention to where it's coming from.

Another Idea given to me would be that it's electrical. Let's think outside the box here. Could it be a hot Coil or a sending unit that is not doing it's job after the bike heats up.
Your thoughts?
Because it does run great when she's cold.

 

Backfiring out the carb indicates a lean idle circuit, as I had with the Sportster I own.

Does the bike run fine while the Enrichener is out? Does the problem start when the (Choke) is pushed in?

This is the scenario I had with my 05 XL883L. I put in the early Sportie needle and richened the Slow Jet to a 48.

 

My Guess is the CPS also known as CPK Crankcase Position Sensor Had to replace two of them on my 04 Sporty.... Gives all the Symtoms you ae describing ...

 

thanks for the input guys, I'll let you know how I make out. Your ideas will give me a good start to trouble shooting this problem.

 

Jay Stronghawk, you nailed it right on the head! I took it to the HD garage this week and asked for a diagnostics check to help find the problem. It was as you said, 'the Crankcase Position Sensor'. She's running like a top now. Thanks for the input guys, hope someday I can help you out as well.