Bad plugs or too lean?

[chef1366]

10.25:1 compression ratio
Stock ignition
Hi-test Chevron
Heat range is 3-3.5 threads.

Thanks for your input.

[49er]

10.25:1 compression ratio
Stock ignition
Hi-test Chevron
Heat range is 3-3.5 threads.

Thanks for your input.

I agree with Lecroy. At 10.25-1 you are running too hot a plug. The fact that you haven't previously had plug problems probably means that you were running too rich in the past and in lower ambient temperatures.

What octane rating is your Hi-test Chevron? You should be running at least 95 octane.
You are running 1150 spec Wiseco Pistons and 1150 carbs. Are you jetting your #2 & 3 pots richer on the mains as the 1150's do? Their stock mains with the airbox fitted are #1 &4 @120 and #2&3 @ 122.5.
Try a new set of D9EA plugs, and go back to 140 mains. And don't believe all the cheap ass's who say how well their GS's run on low octane fuels. They're often not hammering their engines in as extreme conditions as you do!

[lecroy]

Again, where is the timing set and whats the cranking pressure? This will give me an idea of how you have the cam and deck height set. After your little melt, it would be interesting to know the before and after numbers for cranking pressure. Melted parts are never good.

That low a CR is no problem. I think you could run it on almost anything and be good to go (as long as the fuel is set right).

My own experience, 3.5 threads is just asking for it. If you start to see 2 threads, you better be adding more fuel! If the stock ignition is in good working order, your should be fine at this CR. Add more fuel and go with a colder plug. This time just try some 1/8 mile wide open runs and watch the heat line. Best to add a lot more fuel then dial it back. Safer.

I would pull it back apart and recheck the pins (I hate Wiesco pins), crank, pistons (look in the ring landings). Any damage to the crank, send it off. But, this is me. If you do decide to just change the plugs and run it and there is damage, you will get a new lesson on how to lighten your wallet. Your bike, your call.

Good luck.

[rustybronco]

And don't believe all the cheap ass's who say how well their GS's run on low octane fuels.

They even suck with 87 octane in stock form, 37 degrees timing all in @ 2500 rpm what were they thinking?, 4k give it some moderate throttle and rattle, rattle, rattle.... ('82 gs850g)

[chef1366]

Brought the plugs to the dragstrip to show Kris V. He said he's never seen a plug melt while the end electrode stayed perfectly cymmetrical and flat. If it had melted it would be rounded off and the ceramic would be melted.
Bad plugs in my opinion.
Still though I put back in the 140s and went with a D9EA plug. Runs great!

Stock ignition timed stock
The intake and exhaust cams are both set to 110 degrees.

[rapidray]

Bill, I'll bet it will STILL take more fuel if you had 3-3.5 threads on the heat. I'll bet it will run with 145s in it. The D9s are ALL I will use & I don't put D8s in anything but an oil burning, next to dead motor. Also, make sure you don't have more than 34 degrees at FULL advance. Good luck at Yosemite & be safe! Ray.

[chef1366]

I'll keep and eye on the heat range and let you know.
I went down to the 137.5s when I noticed it ran better cold than fully warm when it hit those wonderful 100+ days here in Bako.

The color on the 137.5s looked perfect but I think that was from the needle circuit.

[Shaughn]

A simpler view

This is far less elegant than some of the other theories out there, but did
you gap the plugs using one of these keychain ramp disc feeler gauges?



I've seen them snap off the center electrode before when used ramp side towards the ceramic.
You could have simply cracked it and it fell off in the cylinder, and then the stub got worn as per usual.

Just a thought.
Hey, I've watched a very smart tech absentmindedly gap iridium plugs, making me eat (as service manager) over $100 in plugs.
**** happens.

[chef1366]

I have one similar to that but not the keychain style.

[Nessism]

Brought the plugs to the dragstrip to show Kris V. He said he's never seen a plug melt while the end electrode stayed perfectly cymmetrical and flat. If it had melted it would be rounded off and the ceramic would be melted.
Bad plugs in my opinion.
Still though I put back in the 140s and went with a D9EA plug. Runs great!

Stock ignition timed stock
The intake and exhaust cams are both set to 110 degrees.

Sounds like a reasonable action plan - larger main and cooler plugs. You might want to watch these new plugs closely for the next couple of thousand miles to make sure everything is as expected.

Good luck.

Ed

[chef1366]

Now with WOT I'm getting a second of hesitation before it takes off. I have to do some plug chops.
I wonder if this is ignition related? Have 12 volts at coils but the ignition is stock.
Ray said I should get a Dyna S, green Dyna coils and then jet.

[Nessism]

Now with WOT I'm getting a second of hesitation before it takes off. I have to do some plug chops.
I wonder if this is ignition related? Have 12 volts at coils but the ignition is stock.
Ray said I should get a Dyna S, green Dyna coils and then jet.

Hard to imagine that there is anything wrong with your ignition; it was throwing a spark across a 0.050" gap with those old plugs. Wouldn't hurt to try but seems like an unlikely cause of the problem at this point.

[chef1366]

Have a strange stumble on hard accel. Not at any consistent throttle position.
Decided to strip and dip the carbs cause I did half-a$$ed job the first time. Didn't help.
Pulled the spark plug caps off and snipped the wires back a bit. The wires were black and some were really receded. Didn't get a chance to run it cause it got dark and I have been up since 5am so I'll put the tank on in the morning and do a test ride.

[TheCafeKid]

Have a strange stumble on hard accel. Not at any consistent throttle position.
Decided to strip and dip the carbs cause I did half-a$$ed job the first time. Didn't help.
Pulled the spark plug caps off and snipped the wires back a bit. The wires were black and some were really receded. Didn't get a chance to run it cause it got dark and I have been up since 5am so I'll put the tank on in the morning and do a test ride.

Im having that same hesitation on my 1100G. I was thinking i was lean in the main and maybe a needle shim, but I may check the wires first. Once it passes that lil hiccup, its off to the races. But today, i ran thru some hella storms on my way up to see a friend, and the bike started displaying some "buzziness" afterwards, like maybe it was missing now and then on one cylinder. After it dried out, it smoothed out, but that hesitation is still there, so it may just be some crappy wire/caps...

[49er]

Have a strange stumble on hard accel. Not at any consistent throttle position.
Decided to strip and dip the carbs cause I did half-a$$ed job the first time. Didn't help.
Pulled the spark plug caps off and snipped the wires back a bit. The wires were black and some were really receded. Didn't get a chance to run it cause it got dark and I have been up since 5am so I'll put the tank on in the morning and do a test ride.

Ah, CV carbs. They run so smoothly with an airbox! :-)

Bill, I think that you need to check the operation of the diaphragms. If they're lagging too far behind the engine air/fuel demand, you will have a lean stagger until they open at the right rate. Make certain that part of your pods are not blocking off the vacuum ports.

You can compensate with needle shape, or the diaphragm spring rates.