2008 sportster 1200 backfire/stumbles

[Jack Klarich]

no engine light on, i went to start it and the battery wasnt strong enough to turn it over, i charged it last week and now its at 11.98. if it wont turn the bike over after a week then im getting a new one and see if that helps anything.

That battery is toast, buy a new one and charge it to 12.7 volts before starting the bike, this is probably your problem with the way it has been running
Harley Davidson Forums Run this test with a fully charged battery

 

[dbmg]

If the ECM does not have the proper reference voltage then all kinds of performance issues can and will arise. As Jack has stated the battery is toast.
To many times we check the surface voltage and do not perform a proper load test to really see the lack of ability that the battery has.

 

[Jeff Klarich]

11.98 not good enough, time for a new battery.

 

[T in Texas]

My 08 has the sputtering problem also. It seemed to improve when I cleaned the negitive battery cable on the engine side. But still have the sputter. I have changed the stage one filter, cleaned the idle air controller, installed new plugs, checked plug wires. Still got it. Just as soon as my parts manual shows up I will order a new fuel filter and change that out. While I have the gas tank off, I will attack the intake for any leaks. That's my plan any way!

 

[dbmg]

My 08 has the sputtering problem also. It seemed to improve when I cleaned the negitive battery cable on the engine side. But still have the sputter. I have changed the stage one filter, cleaned the idle air controller, installed new plugs, checked plug wires. Still got it. Just as soon as my parts manual shows up I will order a new fuel filter and change that out. While I have the gas tank off, I will attack the intake for any leaks. That's my plan any way!

When is sputtering happening? Hard acceleration, cruise, parts throttle. Have you checked plug wires for any cracks or signs of arcing to ground. Does bike have fueler to adjust for air filter and changed exhaust if you have ????
Need more info so to avoid a wild goose chase.

 

[T in Texas]

It sputters at a slow speed cruse as in town, going down the street. It picks up speed without missing a beat and runs great on the highway. I am running some seafoam thru it now and will see how that works in time. I bought the bike used in early January from a lot. I am sure they are not Harley dealers or mechanics. It has a stage one air filter which I have replaced and it has some kind of nasty loud exhaust (that I like) other than that all topside gaskets were replaced before I took it off the lot. They went to a Harley dealer in Austin to get the gaskets and new brakes for it.

I don't see any place where the plug wires may be bad but I have thought about replacing them before I remove the gas tank and mess around inside of it. Matter of fact, I will replace them first.

Best guess is that this bike has been sitting for about two years. At least one that I am sure of. That is the reason for the seeafoam additive.

 

[dbmg]

It sputters at a slow speed cruse as in town, going down the street. It picks up speed without missing a beat and runs great on the highway. I am running some seafoam thru it now and will see how that works in time. I bought the bike used in early January from a lot. I am sure they are not Harley dealers or mechanics. It has a stage one air filter which I have replaced and it has some kind of nasty loud exhaust (that I like) other than that all topside gaskets were replaced before I took it off the lot. They went to a Harley dealer in Austin to get the gaskets and new brakes for it.

I don't see any place where the plug wires may be bad but I have thought about replacing them before I remove the gas tank and mess around inside of it. Matter of fact, I will replace them first.

Best guess is that this bike has been sitting for about two years. At least one that I am sure of. That is the reason for the seeafoam additive.

But you have not said about any type of fueler installed. With the combination of high flow air filter and nasty loud exhaust which has little if any back pressure you may have already found the culprit...

 

[T in Texas]

I'm not sure I would no a fueler if I saw one?? I have no idea what all has been installed except what I can see is not stock. Are you saying that maybe the low back pressure is causing the sputter or miss? If it were one of the cars I would swear the timing was off, that is how it acts. Thank you by-the-way for helping me out here...

 

[dbmg]

I'm not sure I would no a fueler if I saw one?? I have no idea what all has been installed except what I can see is not stock. Are you saying that maybe the low back pressure is causing the sputter or miss? If it were one of the cars I would swear the timing was off, that is how it acts. Thank you by-the-way for helping me out here...

Timing is electronically controlled on fuel injected bike. Remove seat and side cover and you may found a box looking electronic device wired in and that would be your fueler... With air and exhaust being what it is you are in a very lean condition that at cruise can cause sputter. Liken it to running out of gas.
I assume there is no check engine light.

 

[T in Texas]

I will check that out in the morning. I have had the seat off once and don't remember anything but the MAP sitting under there. But, I will check that out. No trouble codes, I've checked that a couple of times. Could it be that I am not keeping my RPM's up at low speeds? I have been staying in second gear more now in town to make sure I am not bogging it down. This is my first motorcycle in almost 50 years. I rode much smaller Honda's back then so maybe I am just working on a learning process all over again.