I just purchased an 88 Sportster 883H, the previous owner told me that there was a 1200 kit done to the engine, I am not sure of what pipes are on the bike. the stock pipes were given to me, one of the pieces was wrapped in bubble wrap.. until this bike gets good and warm, the engine will backfire thru the exhaust, if you crack the throttle fast, or when trying to accellerate, not good when a car is coming at you.... but after about 10 minutes of riding it pretty well come out of it. although i did get some seafoam in the tank and filled her up with premium in that time also. it doesnt seem to do it as bad now, but i do let her warm up a bit more now than i did. i was just wondering since the exhaust was put on did they rejet the carb, or would they have needed to? the baffles are still in the pipes. is this something i need to worry about, or just let her warm up good before taking off? I have a couple other things i need to know about this bike, but this is the one that concerns me the most.

josh

 

They would/should have done a re-jet when they did the 1200 conversion. It looks like they threw on drag pipes, which would take away from some of your lower end performance, i.e. a little sluggish when trying to get out of the way from on coming traffic/taking off from a standstill. Also, yes, you'll want some type of baffle with drag pipes to create back pressure for the engine. I'm not sure how long the bike sat before you got it, so running the seafoam through it is a good start to cleaning out the carb to see if that is the problem. There's quite a few things that could be causing this......Exhaust manifold leak, wrong jetting in the carb, leaking carb gasket, etc. To check for a leak at the carb, you can run the bike while spraying some wd-40, (or something else, starter fluid, can't remember right now), around the carb gasket/manifold to see if the idle changes. Someone else will chime in with other, maybe better, suggestion....Just keep asking & we'll help you through it.

 

ya, i didnt figure that the pipes have been on it for very long. they really didnt have any blue on them when i got the bike. that and the front pipe is just kinda hangin there, it not mounted to the frame at all which i need to get fixed. In my shop (i own a boat repair shop) we use carburetor cleaner for checking for vacuum leaks, never thought of trying ether, but i wouldnt want to either. its a little more volatile than i like to use. In the boats we work on here we suggest seafom year-round, so i figured that would be the best place to start. the guy said that there was 600$ dumped into the bike to get it ready for spring, which i have no reciept so i have no idea if anything was even done. i will try the wd-40 or carb cleaner on some spots to see if i can find anything.

Josh

 

Well, you could easily check to see if the carb has been re-jetted by looking to see if the plug has been drilled out....Check the DIY Sticky at the top of the main Sporty Forum page for the Carb Re-jet thread.
Oh, and Yeah, I'd suspect a slight exhaust leak if the pipe is only hanging there by the front mounting bolts & when the engine/pipe gets hot the leak closes slightly from the expanded hot metal. Just a thought.

 

ok i will hopefully have some time tomarrow to check, gotta get the mower goin.. the grass here is a bit tall already.. gotta do the honey-do's if ya know what i mean..

josh

 

well i checked for a leak around the carb with some carb cleaner and didnt find anything. also checked around the exhaust where it bolts to the engine, didnt find anything there either. was backfiring today like it was the other day. once it warmed up good from riding, it wasnt backfiring as much. i guess i am gonna have to dig into the carb now. or try adjusting the mixture. i didnt think to check for the idle mixture adjustment screw though. was too worried about other things. Think i might have broke my big toe on my left foot... hurts like heck, but i still rode, just had to shift a lil different than normal. i'll let you know more as i find out.

Josh

 

it does sound as if you have a fuel air mixture problem. I would check any fuel filter and as stated check the jets. bikes are bad about not wanting to run right till they warm up. at least most I have ever owned have. it is an 88 I suggest letting her idle for a few before starting out. some other things to look for popping on decel, caughing on accel or stuttering. these can be fuel air mixture problems

 

I was looking last night at harley's web site, and i could not find a jet kit. was gonna open up the carb just to make sure everything was clean and i figured if i did not find anything in the carb, then i would try a little bigger idle jet. I let the bike warm up until the jugs feel like they are warm to the touch. i can still hold my hand on them but it is uncomfortable after about 6-7 seconds of continuous contact. so it is getting warm but it still seems to backfire quite a bit. i did notice it almost sounds like its coughing back through the carb too, maybe more of a sneeze, but i definatley am hearing a pop sound from the carb. also if i get the rpm up a bit before i let out on the clutch, it doesnt do it anywhere near as bad. thats why i am thinking the idle jet needs to be a little bigger. actualy the more i think about it, the idle jet may be already too big.. maybe it getting loads of fuel and still trying to burn it up when the exhaust valve opens.. hmm, guess i need to goto a dealer and find a jet kit.. the petcock should have a filter on it, correct? i have not noticed any poping on decel.

josh

 

you need to let all sportsters warm up to operate good,lack of proper warm up can get the rocker boxes leaking!!!!!!!!!!!!!

 

any suggested length of time? i normally have a cig while waiting, so its around 3~5 minutes..

josh