Any of you know anything about carb backfiring?

[mashley]

Hey guys, I know some of you own multiple types of bikes and was wondering if you could give me a hand. I have been working on my girlfriends 04 883 Sportster and it's about to drive me nuts. It has been backfiring through the carb. I adjusted the mixture screw to richen it up and that didn't help. I upped the slow jet one size bigger and played with the mixture now it's running more on the rich side. But it still backfires thru the carb. Carb backfire is usually a sign of lean but it does it running rich as well. Really don't want to take it to the dealership. Wallet is already on the light side as it is. Any help you might could give would be appreciated.

 

Thanks!

[93 venture]

Hummm,Intake valve burnt ,not closing all the way?is it poping back into carb under acceleration

[cowpuc]

Yep,, tight valve lash, burnt intakes can certainly be a cause to the the sympton on this one.. Also check ignition timingmaking sure its spot on - is this model still mechanical advance, if so check it out closely.. Stock single carb or is it twin carb set up?? twin carbs out of sync can also do crazy stuff too..

Now here is another one that I have seen many times but no one around here )my neck f the woods) likes to believe it... Carbon deposits,, uh huh those stupid buildups from running rich OR at high vacuum all the time can and DO cause exactly what your describing too.. The carbon builds up, the carbon gets RED HOT and stays RED HOT in the combustion chamber - fresh fuel/air mix hits it and poof you have pre-det that shows up in a pop on the carb..

another possibility is cam wear,,, I know that HD has had problems with soft cams in the past - have no idea if your model/year was affected by this.. Maybe check the recalls..

Also, let the bike idle and spray the external carb areas with carb cleaner - listen to engine speed changes as you spray the areas where the carb bolts on and so forth. Your are essentially looking for leaks with your spray can.. If you hit a spot where a gasket is gone your engine will pull in carb cleaner and the engine idle speed will change.. This can cause a lean condition and result in a pop - change out any bad gaskets..

Hope it all helps

'Puc

[juggler]

I know that in certain neighborhoods my bike's backfiring can cause gang wars. Darn thing sounds like a gun being fired. Once in a tunnel I was decelerating and it backfired. It sounded like a howitzer cannon being fired.

[rod]

All good ideas so far. On my HD I get carb backfire if the air cleaner is not on tight. Good luck Rod

[SilvrT]

Hey guys, I know some of you own multiple types of bikes and was wondering if you could give me a hand. I have been working on my girlfriends 04 883 Sportster and it's about to drive me nuts. It has been backfiring through the carb. I adjusted the mixture screw to richen it up and that didn't help. I upped the slow jet one size bigger and played with the mixture now it's running more on the rich side. But it still backfires thru the carb. Carb backfire is usually a sign of lean but it does it running rich as well. Really don't want to take it to the dealership. Wallet is already on the light side as it is. Any help you might could give would be appreciated.

 

Thanks!

I worked on my son's '03 Sportster 1200 for the same issue. It was just a matter of getting the mixture screw set right. If I recall, turn it in all the way and then back it out 2 full turns ... fine tune from there (either out more or in more). Seems I recall reading that this is a common problem on these bikes and may not be totally curable. Anyway, this method cured his about 95%.

 

Also, try some SeaFoam.