[Syscrush]

Hey - in the epic (and now closed) "diagnose my bike" thread, you mentioned that with the airbox off you were seeing something that looked like ignition happening in your TB - this gave rise to suggestions that included bad cam timing and arcing from an injector, among others.

A few days ago I was running my bike with the airbox off, and I had disconnected the vacuum line to the petcock from the rear carb. Not surprisingly, I was getting a bit of backfiring from the lean condition on the rear carb - the same kind of cough/sneeze/hesitation you hear at idle on a cold day when the bike needs more choke after starting. I also clearly saw the same kind of phenomenon that you described in your thread.

I would have liked to add this info to that thread, but it's closed. I don't know if it helps you, but I wanted to share in case others were as perplexed as I was about what you described. It appears that this is symptomatic of a vacuum leak or lean condition, not the esoteric stuff proposed in the big thread.

 

[BossMan]

Hey - in the epic (and now closed) "diagnose my bike" thread, you mentioned that with the airbox off you were seeing something that looked like ignition happening in your TB - this gave rise to suggestions that included bad cam timing and arcing from an injector, among others.

A few days ago I was running my bike with the airbox off, and I had disconnected the vacuum line to the petcock from the rear carb. Not surprisingly, I was getting a bit of backfiring from the lean condition on the rear carb - the same kind of cough/sneeze/hesitation you hear at idle on a cold day when the bike needs more choke after starting. I also clearly saw the same kind of phenomenon that you described in your thread.

I would have liked to add this info to that thread, but it's closed. I don't know if it helps you, but I wanted to share in case others were as perplexed as I was about what you described. It appears that this is symptomatic of a vacuum leak or lean condition, not the esoteric stuff proposed in the big thread.

Do you think it's possible that it was running lean because his air box was off?

He said he checked vacuum hoses right? I don't really remember.

 

[Syscrush]

Do you think it's possible that it was running lean because his air box was off?

He said he checked vacuum hoses right? I don't really remember.

In that thread it seemed like he had checked everything. I doubt that the problem was because of having the airbox off, because mine ran fine with the airbox off (idling, at least) - it was only when I had the vacuum leak that it did this. When I covered the nipple with my finger, the coughing/backfiring stopped immediately.

I posted this in part in the hopes that it might help ACS with his bike, but also because when he described the symptom it seemed that nobody had seen it before and the suggestions that resulted were a lot more wild/esoteric than what it really takes to cause this kind of problem.

 

[BossMan]

Well that would make sense.

On my old GS there were little O rings between the intake and cylinder head that would wear out and allow air in. The bike would run like crap until they got replaced.

http://fiche.ronayers.com/Index.cfm...650S/GroupID/250808/Group/FRONT_CYLINDER_HEAD

That would be part #15 on the fiche here. I wonder if his are worn out? I mean he does have a LOT of miles on that bike.