Arcing from throttle cable to frame.

[NickNoo]

Have just been checking the carbs with the fuel tank off the bike. I noticed a crackling sound when the engine was running and traced it to a spark arcing from the throttle cable to the frame, just above the coils (about a 10mm gap) ! It seems to arc in time with the coil (ie about 10 times a second at tickover).
With the fuel tank in place, the spark would probably be striking the tank itself - hmmm .. not good !
Anyway, I found that the carbs themselves are NOT earthed and that may have something to do with the problem - so I wired up an earth from one of the carb cap bolts to the airbox.
This has stopped the arcing, but I am still concerned that there may be a bigger underlying problem eg with the ignition system ?

I have had a look at the manual and there is no mention of an earthing strap on the carbs, so I assume that Suzuki did not earth the carbs on these bikes.

The bike is stock apart from Bandit coils, Dyna S ignition system, replacement R/R and new plug caps fitted a year ago.
The bike runs fine, with no obvious ignition problems.
Anyone else had this problem ?

[RacingJake]

Could be a high tension lead problem or coil. Check all the wiring to the coil and leads. You could hook up a ground wire to a screwdriver and slowly past it over the coils and leads to find out where the leakage is.

[SqDancerLynn1]

Replace the coils with some thing from a later 90's model bike
Bandit, GSX, RF900

[bwringer]

Sounds a lot like a bad spark plug wire. A very bad spark plug wire.

Take the tank off and look for a chafed area on one of the plug wires.

[KEITH KRAUSE]

Why would you want to use a part that contains fuel as a ground??
Carbs shouldn't be grounded. Don't try a band-aid fix on this. Dangerous!
I don't know what's wrong but if you saw the arc coming FROM the cable TO the frame, then there's obviously voltage in the cable, caused by a hot leg contacting the cable somewhere.
Check for the harness contacting the cable anywhere. If not, then there must be contact at the throttle housing which involves the kill switch. This should blow a fuse but the harness could be butchered by a PO and you may have no fuse protection or something else going on?

[focus frenzy]

Why would you want to use a part that contains fuel as a ground??
Carbs shouldn't be grounded. Don't try a band-aid fix on this. Dangerous!
I don't know what's wrong but if you saw the arc coming FROM the cable TO the frame, then there's obviously voltage in the cable, caused by a hot leg contacting the cable somewhere.
Check for the harness contacting the cable anywhere. If not, then there must be contact at the throttle housing which involves the kill switch. This should blow a fuse but the harness could be butchered by a PO and you may have no fuse protection or something else going on?

it is going to be a ignition problem, 12 volts (closer to 14) won't arc across a 10mm gap, but 35,000 volts from a coil will and the throttle cable runs down across one of the coils.

[KEITH KRAUSE]

Well, I just took his words literally. He said from the cable to the frame and it appears he was watching it for some time.
It probably is the coil failing as suggested.
My main reason for my first reply was the thing has to be fixed correctly. Using the carbs for grounding isn't right.

[NickNoo]

Thanks for the comments - it does look like a loose spark plug wire from the RHS coil. Have replaced the coil and removed the ground to the carb as suggested.
Seems to have cured the problem, hopefully for good.