Nearly at my wits end with this bike. Idle takes off like a rocket with the tank on.

[uk gs nut]

Sucking air from the vacuum feed to the tank is my thoughts

[cp___32]

Thanks everyone!

I'll do a thorough inspection of the throttle cable to make sure it's all good and tighten it down at the adjuster. If that doesn't work I've got some spare fuel tubing around so I'll replace the vacuum line that operates the petcock. And if all else fails, I like the idea of leaving the tank in place and still running the aux fuel supply. If that fixes it then I know it's fuel delivery so I'll troubleshoot from there.

Gotta do the strut mount and front brakes on my car but hopefully I'll get to the GS on the weekend and give those things a try. I'll report back soon.

Thanks

[cp___32]

Tightened up the throttle cable, and decided to check the plug order. Turns out that I had 2 and 3 swapped so when I changed them to the correct configuration it ran better.
Just to see if it was a timing issue I decided to hook up my timing light and found something curious.

My bogging and random stalling as well as my idle issue might be spark related. I noticed that at idle the timing light was flashing really inconsistently and that matched exactly with the misfire/bogging I was experiencing. Then it would catch and flash as expected and the revs would take off. Then suddenly the spark would go inconsistent and the revs would drop again and it would idle rough. Sometimes the spark would stop entirely (at high RPM and idle) and the bike would die. The best I can explain it was the spark looked like Morse code.

The coils were new OEM replacements as were the plug wires. I'll look up how to test the coils to make sure they are good. I'm guessing I could have a grounding issue? It might also explain why the bike would crank no problem and then sometimes it would be completely dead as if the key wasn't on. Pressing the starter switch would not do anything but I could jump across the starter terminals and the bike would crank. That seems the most logical explanation, no? If I can get consistent spark I think it'll solve my problem. More late nights searching the forum for answers this weekend

[salty_monk]

Are you using the stock 80 Spark box? No mechanical advance? They have been known to be faulty..... The fix is to get a Dyna or similar & a mechanical advance (or run a Dyna 2000).

Also the revs could take off with a faulty petcock... if it runs lean the revs would rise at idle.

[cp___32]

Oh, I tried running the bike without the gas cap on. Forgot to mention that. I heard the petcock clacking away and when the bike would misfire I would notice the petcock would also not get a pulse. I'm assuming that's normal?

Yeah pretty much all the electrics except the wiring loom itself are new. SSPB, Dyna-S ignition, I can't recall the brand but the stator is new. Picked up one of the fancy R/Rs used on Polaris quads and R6s and such. OEM Coils like I mentioned, NGK plug caps. New Champion plugs. I probably should have sprung for the Green Dyna coils when I replaced them.

[tkent02]

The petcock clacking away is not normal, it should be silent.

[cp___32]

With the gas cap off, I could definitely see the fuel sloshing around as the vacuum pulsed the petcock and could hear the noise reverb through the tank (which was 1/2 full at the time). I put a new rebuild kit in it a few years back and this is the first time I've had the tank on it with fuel in it. Maybe it wasn't the noise from the petcock itself but engine noise being amplified by the tank? It doesn't seem to be starving for fuel either.

I'll check the coils and grounds this weekend and see if I can get consistent spark and go from there.

[mmattockx]

Tightened up the throttle cable, and decided to check the plug order. Turns out that I had 2 and 3 swapped so when I changed them to the correct configuration it ran better.

2 and 3 fire together so it shouldn't matter if you have them swapped or not.

With the gas cap off, I could definitely see the fuel sloshing around as the vacuum pulsed the petcock and could hear the noise reverb through the tank (which was 1/2 full at the time).

Does the petcock make noise when set to the 'prime' position? Do you get the same revving problem?


Mark

[Connorjeanes]

Mine is doing the same thing although mine is on VM Carbs, and having the tank on or off makes no difference! Let me know if you have any luck!

so frustrating! If I drop the idle screw all the way out so I keep it running on the throttle she rides lovely loads of power. But obviously no idle will just stall on closed throttle.

good luck!