https://www.hdforums.com/forum/engin...uns-rough.html - old thread about bike

1986 1100cc Sportster Evolution -

Well I recently had a post asking for help because out of nowhere my sportster started running really rough (backfiring, stalling, running on one cylinder) for no apparent reason. The posts where helpful but the problem still persists, most posts attacked fuel problems but I have troubleshot that entire system and am sure it is getting the fuel it needs.

So now I guess I am onto the electrical/ignition system. The timing seemed to be fine when it ran well and it has not moved, I tried replacing the plugs in case they were fouled and that did not help. I replaced the spark plug wires and that did not help, did a spark test once and it seemed to have spark at both plugs (the spark it needs I am not sure). So since the rear cylinder seems to be the one not firing I suspect it is a bad ignition coil not throwing the proper spark to the rear cylinder. Anyone else have any ideas? I am open to anything, and am tired of not seeing this bike in motion!!!!

 

Don't know if you found your problem or not. I'd replace intake manifold gaskets. this could be your problem.

 

Well I sprayed starting fluid on the gaskets all around that area while it was idling. I got no change in rpms so that seal is good, forgot to mention that.

 

what about a fuel management device? got one? if so I would rule that out first as it will certainly affect everything, fuel, spark, electrical, etc.

 

sounds like the exact problem im having on a 95 sportster 883....im trying everything.....it sometimes runs better on choke

 

Everone was telling me its a carb issue. So i swapped it out with another carb and it has the same issues.....Hope to figure it out soon...summers passing quick

 

Do you have a dual-fire or single-fire ignition? Have you checked the resistance of the primary winding in the ignition coil?

 

i had something like that happen on my 84 tourglide,it would run fine till it warmed up then start spitting and backfire then run like it was on one cylinder, went though about everything you did and found out it was the ignition module, put one in that goes in the nose cone and ran great after that, even better than before

 

i dont think my problem is electrical....because it runs an rides okay with the choke pulled out with just the occasional sputter...but push the choke in and it wont take any throttle what so ever....

 

and Dane,,,,if you find your solution,,,,please let me know