One black plug, 3 good ones...

[hikermikem]

My '82 GS850GL is offically back on the road now,after a 15 year sleep !!! Still sorting out a few issues though - it seems to run quite well considering i haven't sync'ed the carbs yet. My lousy Motion-Pro unit is giving me trouble (another story for another time).

I've cleaned the carbs, replaced o-rings, sealed the airbox, etc... Bike starts well & idles at 1K no problem. I've pulled the plugs & I noticed #3 is always black & sooty. The others look very nice, kinda tan with no hint of soot.

I switched #2 plug with #3 to rule out a bad plug, and it isn't the plug - #3 still got sooty.

Everything is stock, with the exception of a K&N drop in air filter.

I've played with the mixture screws (all approx. 3 turns out) & the idle is good. I used a Morgan colortune plug to set the mixture screws, but it seemed to want to be at 4-5 turns, so i abandoned that & set them by ear (become one with the bike, grasshopper...)

What might be the reason the #3 clyinder is apparently so rich? Would a carb sync fix this? Please head me in the right direction.

Thanks for any thoughts you want to share!

Mike

[TheCafeKid]

My '82 GS850GL is offically back on the road now,after a 15 year sleep !!! Still sorting out a few issues though - it seems to run quite well considering i haven't sync'ed the carbs yet. My lousy Motion-Pro unit is giving me trouble (another story for another time).

I've cleaned the carbs, replaced o-rings, sealed the airbox, etc... Bike starts well & idles at 1K no problem. I've pulled the plugs & I noticed #3 is always black & sooty. The others look very nice, kinda tan with no hint of soot.

I switched #2 plug with #3 to rule out a bad plug, and it isn't the plug - #3 still got sooty.

Everything is stock, with the exception of a K&N drop in air filter.

I've played with the mixture screws (all approx. 3 turns out) & the idle is good. I used a Morgan colortune plug to set the mixture screws, but it seemed to want to be at 4-5 turns, so i abandoned that & set them by ear (become one with the bike, grasshopper...)

What might be the reason the #3 clyinder is apparently so rich? Would a carb sync fix this? Please head me in the right direction.

Thanks for any thoughts you want to share!

Mike

Carb sync would help, tho you may try backing off number three on the mixture screw. Also, WHEN is this problem occuring? Have you done plug chops? It could be NOT in the idle circuit and somewhere else...

[hikermikem]

Carb sync would help, tho you may try backing off number three on the mixture screw. Also, WHEN is this problem occuring? Have you done plug chops? It could be NOT in the idle circuit and somewhere else...

Hey there TCK, how's things?

No, haven't done a proper plug chop yet - just notice that #3 is ALWAYS black & sooty, while the others look good. Oh yeah, I can see the color on the exhaust pipe for #3 isn't as gold as the other 3 pipes either.

Maybe a bad plug cap?

thanks

[TheCafeKid]

Hey there TCK, how's things?

No, haven't done a proper plug chop yet - just notice that #3 is ALWAYS black & sooty, while the others look good. Oh yeah, I can see the color on the exhaust pipe for #3 isn't as gold as the other 3 pipes either.

Maybe a bad plug cap?

thanks

Possible. Clearly its isolated to that cylinder, so you know that you have a spark/fuel problem there. In tinkering and learning from Steve on the CV type carbs, I found that they are less likely to have the adjustment screws in the same position as the VMs for some reason. For instance, on my former 1100G, cylinder 1 was at 2.75 turns out, cyl 2 at 2.25 turns out. Three might have been 2.5. I would suggest a simple try at this, to find out if THIS part of your fuel system is the culprit. Turn the number three screw all the way back in to light seat. Then turn it out till the bike idles at the highest point, when it ceases to climb in idle, thats where it wants to be. Listen closely, and go slowly, allowing the motor time to catch up to your adjustment. If this doesnt clean the plug up, check for good spark. Check your gap too... lots of suggestions, but this is the simplest and quickest to eliminate.

[hikermikem]

Possible. Clearly its isolated to that cylinder, so you know that you have a spark/fuel problem there. In tinkering and learning from Steve on the CV type carbs, I found that they are less likely to have the adjustment screws in the same position as the VMs for some reason. For instance, on my former 1100G, cylinder 1 was at 2.75 turns out, cyl 2 at 2.25 turns out. Three might have been 2.5. I would suggest a simple try at this, to find out if THIS part of your fuel system is the culprit. Turn the number three screw all the way back in to light seat. Then turn it out till the bike idles at the highest point, when it ceases to climb in idle, thats where it wants to be. Listen closely, and go slowly, allowing the motor time to catch up to your adjustment. If this doesnt clean the plug up, check for good spark. Check your gap too... lots of suggestions, but this is the simplest and quickest to eliminate.

Thanks for the suggestions - I did actually mess a bit with the #3 mix screw before, didn't seem to make much difference. After a proper carb sync I'll try again to set the mix screws better.

[Steve]

One thing to verify before you go twiddling with the screws ...
you are counting from left to right? That is, from clutch hand to throttle hand?

I ask that because if you are counting the other direction, your #3 (actually #2) is the one connected to the petcock vacuum. If the petcock diaphragm has a leak, it will foul out the plug rather easily.
Earlier VM carbs get the vacuum from #3, but the CV carbs get it from #2.

.

[hikermikem]

One thing to verify before you go twiddling with the screws ...
you are counting from left to right? That is, from clutch hand to throttle hand?

I ask that because if you are counting the other direction, your #3 (actually #2) is the one connected to the petcock vacuum. If the petcock diaphragm has a leak, it will foul out the plug rather easily.
Earlier VM carbs get the vacuum from #3, but the CV carbs get it from #2
.

Yeah, I have the cylinders numbered correctly - new OEM petcock installed as well, during the 3+ month restoration period.

Thanks for the input though...

[TheCafeKid]

Yeah, I have the cylinders numbered correctly - new OEM petcock installed as well, during the 3+ month restoration period.

Thanks for the input though...

When you rebuilt them, did you check your float valves? I wasnt aware of how easily they foul untill Steve enlightened me. If they've developed a scored ring around the needle, its probably toast. If so, it may be passing more fuel than that cylinder needs. But again, that would require a tear down of the carbs to find. Try the other things, and see if that helps atall, if not, then you know where to look next. Fortunately, since its only that one cylinder, it shouldnt be difficult to track down. You sound like you're very close.

[hikermikem]

When you rebuilt them, did you check your float valves? I wasnt aware of how easily they foul untill Steve enlightened me. If they've developed a scored ring around the needle, its probably toast. If so, it may be passing more fuel than that cylinder needs. But again, that would require a tear down of the carbs to find. Try the other things, and see if that helps atall, if not, then you know where to look next. Fortunately, since its only that one cylinder, it shouldnt be difficult to track down. You sound like you're very close.

I rebuilt the carbs & installed all new needle valves & seats. I set & double-checked the float heights, raised the jet needles a "notch" and POR'ed the fuel tank. My bench synch was very precise too.

Lots of new bits & such as well...

It's been a fairly long road getting this bike back to road-worthy status, and I'm the type of guy who generally does things the right way, even if it means taking longer & spending more money.

Like I stated earlier, I'm still sorting things out, but was struck by the fact the #3 plug is consistently black at the outset.

[TheCafeKid]

I rebuilt the carbs & installed all new needle valves & seats. I set & double-checked the float heights, raised the jet needles a "notch" and POR'ed the fuel tank. My bench synch was very precise too.

Lots of new bits & such as well...

It's been a fairly long road getting this bike back to road-worthy status, and I'm the type of guy who generally does things the right way, even if it means taking longer & spending more money.

Like I stated earlier, I'm still sorting things out, but was struck by the fact the #3 plug is consistently black at the outset.

Cool, was just asking. Not discrediting your efforts. I am guilty of overlooking little things like that myself sometimes, so I try to always go thru everything two or three times in my head to assure i got it right. One of these days, I will get organized, and actually make up a list of proceedures for myself. I work better when I have a set list of tasks. Im a bit ADD i think...lol.

At any rate, If your not finding that fuel seems to be the culprit, I could only then suspect ignition/spark. Not the coil, as they dont go half out, so cap could be suspect, gap could be suspect, as well as the plug itself. Maybe its bum. Been known to happen.

[TheCafeKid]

I rebuilt the carbs & installed all new needle valves & seats. I set & double-checked the float heights, raised the jet needles a "notch" and POR'ed the fuel tank. My bench synch was very precise too.

Lots of new bits & such as well...

It's been a fairly long road getting this bike back to road-worthy status, and I'm the type of guy who generally does things the right way, even if it means taking longer & spending more money.

Like I stated earlier, I'm still sorting things out, but was struck by the fact the #3 plug is consistently black at the outset.

Wait...this is an 82 that you said was stock. How did you raise the needles? If you used washers, I may have a source of your problem....

[chef1366]

Are you sure the rings seated after 15 years of sitting. Check compression.
If the rings aren't sealed ride the p!ss out of it until they do.

[hikermikem]

Wait...this is an 82 that you said was stock. How did you raise the needles? If you used washers, I may have a source of your problem....

Yes, I used washers on all 4 carbs, but only #3 is black.

[hikermikem]

Are you sure the rings seated after 15 years of sitting. Check compression.
If the rings aren't sealed ride the p!ss out of it until they do.

Good idea, I haven't checked the compression; I have a compression gage so I will do that...

thanks bill

[Nessism]

Hey Mike,

How about making one of those fuel height gauges they show in the factory manual and verifying the fuel level in that #3 carb? Another thing to try is switching number 2 and 3 plug caps to see if the problem follows the cylinder or the plug cap (both 2 and 3 fire at the same time). Could be you have a bad cap or bad wire.

Good luck.

Ed