What's my next move - #3 plug STILL BLACK !!

[hikermikem]

I've brought my GS850GLZ back to life after a long sleep - done all the suggested work, and then some:

dipped the carbs
replaced o-rings
vac-sync'ed the carbs
raised/shimmed jet needles the equivalent of 1 notch
sealed airbox / drop-in K&N filter
adjusted valves
coil relay mod
new Dyna coils (3 ohm) & wires
rebuilt cam chain tensioner
cleaned ALL electrical contacts
compression check (all cylinders >150#)
...other stuff I can't recall at the moment...

Bike starts great & idles at 1K great.

However, I seem to be fouling a plug (#3) after a bit. I can feel it start to unbalance & vibrate at highway speed, and can also feel a slight stumble at the lower RPM's. When I get home & pull all the plugs, 1,2, & 4 look good - #3 is ALWAYS jet black (see pic attached).

I've played with the mixture screw to no avail, experimented with changing the shims on the jet needles -nada.

I put new coils & wires on yesterday, as I was convinced the 2/3 coil was intermittent. Didn't seem to help, I can feel (and hear) the engine only running on 3 cylinders.

I'm assuming the ignitor is good, because I'm thinking it couldn't fail just #3 without taking #2 with it (is that correct?)

I just put a brand new plug in #3, in the hopes I may have a bad plug (that would be too easy.)

I need some sound advice as to what to do next - I really don't want to take the carbs off & reclean but I think that may be my next move...

What say all you??

[chef1366]

And I think I chase my tail sometimes.
Have a look at the needles and needle jets and make sure they are the same part numbers and not worn.
Does look like fuel though. Any chance it's oil?

[49er]

What Chef said, plus did you check the condition of the needle valves while you had the carbs apart. If the tips are worn, that will cause flooding. They also have a washer that the assy seats on. If you accidently left that off #3 valve, it will be causing the float to let more fuel into the bowl than is ideal, causing that carb to run rich, especially down low in the rev range.
Did you set all the floats at the correct height before re-asssembly?
That plug looks rich to me. Oil leaves a more shinny black film on the plug base.

[lucabond]

Did you try swaping the plug wires on 2 and 3 just to rule out the coil or spark plug wire. I dought its this but I had a plug that looked just like that but it was my #4 I was poking around and found in my haste to put it back together I forgot to tighten the clamps on the boots from the air box to carbs they were just sitting there. I also had a exhaust leak where the #3 and #4 pipes come together which I just got sealed. After fixing both of those probems I went for a 70 mile spin yesterday came home pulled the #4 and it looked like the other plugs. I supect it was more the exhaust leak throwing things out of balence than the loose clamps. But I dont get the little back firing noise I used to before I tighten the clamps. I guess this is just food for thought. Good luck

[hikermikem]

And I think I chase my tail sometimes.
Have a look at the needles and needle jets and make sure they are the same part numbers and not worn.
Does look like fuel though. Any chance it's oil?

I checked all the component p/n's when it was apart - no differences.

Not sure I could tell if things are that worn, but all jets & seats the same ans only #3 is black.

[hikermikem]

What Chef said, plus did you check the condition of the needle valves while you had the carbs apart. If the tips are worn, that will cause flooding. They also have a washer that the assy seats on. If you accidently left that off #3 valve, it will be causing the float to let more fuel into the bowl than is ideal, causing that carb to run rich, especially down low in the rev range.
Did you set all the floats at the correct height before re-asssembly?
That plug looks rich to me. Oil leaves a more shinny black film on the plug base.

Yes, I thought of this - forgot to document this in my initial expalnation, but I actually checked the fuel level (not float height) in the #3 bowl. It was spot-on at 5mm.

I also replaced all the needle valves when i rebuilt the carbs.

I'm wondering, perhaps a mis-sized main jet??

Thanks

[dardoonk]

Had a similar problem. If your using after market K&L jets, swap them out for actual Mikuni jets.

On another note, double check the timing on both the 1-4 & 2-3 pickups for the Dyna ignition. I found they were not set correctly out of the box and had to make adjustments to both rather than just adjusting the whole plate like you would normally do.

[flyingace]

I had a similar problem with my #4 cylinder. Maybe this applies to your #3.

Remove the #3 airscrew (top, engine side of carb) and look at the components. That consists of screw, spring, washer and o-ring. Check for corrosion of the spring and washer. Water can sit in the recess of the air-screw and leak into it.

That corrosion can get in the passages and plug things up in your idle and off-idle circuits. This eventually fouls the plug. You can clean the passages and think your problem is solved, but the corrosion continues and it happens again.

If you find corrosion, spray out the circuits with carb cleaner and compressed air and replace the corroded items.

[hikermikem]

Had a similar problem. If your using after market K&L jets, swap them out for actual Mikuni jets.

Yes, I do believe I will do that - Chef warned me of those K&L main jets long ago & I didn't listen. Would be sweet if this fixes the issue...

On another note, double check the timing on both the 1-4 & 2-3 pickups for the Dyna ignition. I found they were not set correctly out of the box and had to make adjustments to both rather than just adjusting the whole plate like you would normally do.

I don't have a Dyna S ignition installed - just the Dyna coils for now; although I do have one sitting here in a box I bought last year...

Thanks for the suggestions...

[hikermikem]

I had a similar problem with my #4 cylinder. Maybe this applies to your #3.

Remove the #3 airscrew (top, engine side of carb) and look at the components. That consists of screw, spring, washer and o-ring. Check for corrosion of the spring and washer. Water can sit in the recess of the air-screw and leak into it.

That corrosion can get in the passages and plug things up in your idle and off-idle circuits. This eventually fouls the plug. You can clean the passages and think your problem is solved, but the corrosion continues and it happens again.

If you find corrosion, spray out the circuits with carb cleaner and compressed air and replace the corroded items.

Thanks for the suggestion. Actually, i had removed & cleaned ALL the mixture screws when I dipped the carbs earlier this Spring. You're right, they were pretty well crudded up... Nice & clean now though.

Thanks,

[flyingace]

If there was crud, dipping won't be enough. You HAVE to use spray cleaner and compressed air.

[Steve]

My only suggestion goes back to basics before we all "assume" something.

Are you counting cylinders from left to right? That is, from clutch hand to throttle hand?

If so, I can only suggest going back and checking details. If you are counting in the other direction, it might be the petcock diaphragm.

.

[hikermikem]

Are you counting cylinders from left to right? That is, from clutch hand to throttle hand?
.

Jeez Steve, I'm not THAT inept !

I just finished taking the carbs off & replacing the main & pilot jets with Mikuni jets. I did some carb passage spraying & compressed air blowing as well to be on the safe side. If this doesn't work, then I guess I'll be re-dipping again.

Thanks for all the suggestions.

Mike

[hikermikem]

Well... changing the jets didn't work - still got a black plug !!

I'll let it sit overnight & tomorrow night I'm going to re-check the valve clearances. Depending on what i find, I would guess re-dipping is next.

Just thinking about ALL possibilities - if its oil fouling, what is the most likely reason?? The compression is very good, >150#.

I'm not a good enough "backyard mechanic" to know

Thanks,

mike

[Nessism]

Valve stem oil seals can get hard and leak with age. Oil control rings also sometimes stick. Is the bike fouling plugs? Wonder if the choke could be hanging up and leaking gas inside the carbs? Did you check the slide diaphragms?

If it's not fouling the plug, Seafoam and a B7 plug might be worth a try.

Hope you figure it out.