Topic: 1981 XS1100 special - trouble shooting.

[Shenanigans]

Got a friend with one that I am trying to figure out the problem. I have "worked" on the bike once with no tools so yeah...

It wont run right and is hard to start as it backfires (both carb side and pipe side) between 0 to about 2500 rpms. From all 4 cylinders. Anything above that and the bike runs normal, responds well. My first thought was maybe a stuck advancer so he took it off and lubed it. He claims its better but is still doing the same thing. I checked the carbs and they are clean.

I relized this info is pretty vauge but was wondering what I should look out for. Not as familar with these bikes but you got to learn one way right!

I am heading over there in a hour for round 2

[gane]

S, Possibly the #1 problem with the xs1100 was it's advance unit.....or, more accuratly, the spagetti wires from it to the wire harness. if you pop the pick-up cover & start the bike you can see the vac advance "module" shift w/rpms. put a little stress on the wires exiting it & see if your' problem goes away... luck G

[Shenanigans]

Well had a chance to look at it a bit.

The bike acts a bit erratic in the entire rpm range. The vaccum advancer seems to be working, or at least moving if the bike manages to get in the higher rev range. The bike bike seemed to fire very erratic. I put the timing light on it and it was all over the place. No matter how much I moved in in either direction the timing would be jumping everywhere. So I could not time it at all. I held down the vaccum, advancer then tried to time it (just to see) and there was no change. Timing still all over the place.

I tried moving and jiggling all the wires like you had suggested and it had no effect.

Why in the hell does in have a mechanical AND a vaccum operated advance unit?

[bryanj]

Can't remember for certain but i have a vague memory that the vacuum unit retards the timing