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

[Guest]

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??

 

[Guest]

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

 

[Guest]

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.

 

[Guest]

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.

 

[Guest]

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...

 

[Guest]

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.

.

 

[Guest]

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

 

[Guest]

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.

 

[Don-lo]

If your compression on that cylinder is 150, valves are not the problem. Possible fuel problems would be drilled/gouged pilot jet (can be checked by swapping pilot jets with another cylinder), plugged air jet, leaking needle seat o-ring, jet needle too high (loose/no spring/wrong spacers) or damaged/misadjusted choke plunger. A bad diaphram would make it run bad, but not sure if would foul a plug. You need to narrow down the search. Warm the bike up, shut it down, put a new plug in #3, start it up and IDLE ONLY for 30 seconds. Shut it down and check the plug. This should let you know if it is in the idle circuit or not.

TOO MUCH FUEL is the usual culprit, but LACK OF AIR/AIRFLOW is the same thing. I have seen things like plugged/crushed air snorkels or crushed header pipes cause this.

Oil black is a little shiny. Possible causes are head gasket, valve seals, and oil rings.

 

[Guest]

I don't know if it's fouling plugs really - I think it is because I can feel the difference in the engine - meaning it feels like it's running on 3 cylinders. Especially noticable at highway speeds >75.

The choke rail seems quite free, slides open & closed with no difficulty. The bike doesn't smoke at all either - starts right up, idles nice at 1K - seems to run quite well up to about 65 or so.

I come home, pull #3 plug & it's black & sooty. I brush it clean with a wire brush & put it back, only to repeat the process the next day.

I checked the diaphram too - no rips, tears or leaks.

 

[Don-lo]

The choke rail can slide easily but have you inspected how #3 plunger looks? Is it dropping all the way back down? Did you take the plunger out and look at it? There is a hard rubber bottom to it, and I have seen crud accumulate there, thus allowing extra gas to flow.

 

[Steve]

Jeez Steve, I'm not THAT inept !

Not saying that you are inept, it's just that some people still don't know which way the cylinders are numbered.
I did not think you were one of them, this was intended more as a reminder to the newbies that don't know that little tidbit yet.

.

 

[KEITH KRAUSE]

I can't tell if that plug pic looks oily or just sooty from a rich mixture. I'm thinking rich because you don't mention seeing any whitish smoke and you said compression was good.
I'd probably back up a bit and with one of the other plugs I'd verify good spark. If the spark looks the same at 3 as it does at 4, I'd blame the carb.
Considering what you've already tried, I'd try different throttle settings followed by a plug check to see if you can narrow it down to the main jet, jet needle or pilot circuit. I think you said it seemed to run fine until 65 or so(?). If so, then that suggests the pilot circuit is OK and maybe it's the jet needle or main jet.
Before testing, one thought is the primary air jet could be clogged/semi-clogged? The primary air jet controls air flow while operating in the jet needle and main jet circuits. It supplies air through a passage that leads directly to the jet needle/needle jet. Don't just blow high pressure into it and call it good, VERIFY where the air is exiting and that it appears to be 100% clear. Study a CV carb illustration and you'll know right where to feel for exiting air. Compare that flow to one of the carbs that isn't giving you any trouble.
After that, a rich mixture could be other things if carb related. Worn needle jet, jet needle, dirt/varnish build up in the tiny holes in the needle jet/bleed pipe, leaking o-ring, incorrect jet size, etc.