When you're all out of ideas, turn the lights off

[Guest]

Hey guys, quick story I wanted to share with you guys.

I've been slowly restoring my 81 gs550t that I got off craigslist. I tore down the carbs, dipped em, rebuilt them, replaced the tires, chain, regulator rectifier, intake boots..you get the point

It's been running great!...until two weeks ago my bike wouldn't idle. When it got under 1500 rpm it would stumble, sometimes severly enough to stall.

I checked for everything, vacuum leaks, bad plugs, resynched my carbs (i did both bench and used the gauge sync tool when I rebuilt them) used color tune to check my idle mixtures (about 3 turns out), checked voltage at coils spark at all the plugs. Everything was fine...

I was just about ready to pull my carbs off and re dip them thinking my idle circuit was clogged.

So I'm sitting in my garage next to my bike while it's idling poorly, accepting that I'm gonna have to start from square 1 again with the carbs, when the lights automatically shut off on the garage motor.

Then I see it. On the left most cylinder, the spark is jumping from the bottom of the boot, to the hex part of the plug!

I took a video to show you guys. Happens right in the beginning:

I was so happy and confused at the same time. I finally found the problem after two weeks of struggling.

I took out the plug and this is what it looked like:

IMG_20150917_195924.jpg

You can see right to the left of the B a dark dot. That looked like where the spark had burned the ceramic.

Thinking it was a faulty plug, I replaced it (NGK B8ES) and after about 4 minutes of idling perfectly, the arcing started again, in the same spot

So my question is how do I go about replacing the boot? Could a faulty boot be causing this? Or is it something else? It seems to only happen most at idle.

Sorry for the long post guys, just wanted to share my experience with you all in case someone is having a similar problem.

Thanks for looking

[bonanzadave]

Get some NGK Plug boots anywhere you buy motorcycle parts. Take note, there are different angle caps and you may have a couple different ones. (ie: 1&4 vs 2&3). Cut off the old caps, screw on the new caps. Easy. Should be mandatory every 10 years or so. Probably find a couple tutorials here if you search NGK or plug caps. Nice find BTW......

[tkent02]

That's very common, the boots are easy to replace. Get the original NGK ones, someone like Z1 stocks them. Take your old boot apart, maybe it's something you can fix. Could be the spark wouldn't be arcing where it is if the normal path through the plug was working better. There is a tiny resistor in there, sometimes it gets corroded. You can replace it with a piece of wire. Maybe the rubber bit is cracked allowing the spark to jump out, on one of mine that was repaired with electrical tape. Years ago. It's working fine still.
Cut a 1/4 inch of the end of the spark plug wire off, it's probably corroded too.

[bonanzadave]

Cut a 1/4 inch of the end of the spark plug wire off, it's probably corroded too.

Yes that. Here ya go.....

"That's it. I told you it was simple"

BassCliff

[jetmike747]

Sweet, thank you guys! I just ordered the new NGK boots, two of each different angle like BassCliff used. You guys are awesome, thanks again for the help!

[60ratrod]

That's how i found a hole in the coil boot on one of my cut to length wires for my dyna coils. I also heard an electrical pop. Also, don't test for spark on the carbs. I was testing out my sspb after getting it installed and didn't notice i had the plugs laying on the carbs until spark was jumping out of the throttle cable at my face

[OldVet66]

until spark was jumping out of the throttle cable at my face

That will get your attention.

[Brendan W]

Remember the shiny metal covers on plug caps ?

[60ratrod]

Especially when it's the strong purplish-blue spark. I've been hit a few times by spark over the years, the first time being my stepdad trying to get a chainsaw going and says, "here, hold this".