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

[Guest]

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.

Thanks for weighing in Keith - I am in the process of now working through all the carb variables you mentioned. I've ruled out spark because I've already covered that "with a blanket" - coil mod, new Dyna coils & wires, charging system OK... spark is nice & blue on all 4.

I just replaced the mains (115) & pilots (40) with geniune Mikuni parts, and also blew out the air pilots (180).

I have previously dipped & replaced o-rings on these carbs (my 3rd set), but I know they still MAY be plugged. However, I'm pretty sure I did a good job butI know it's possible it wasn't good enough...

I think tonights exercise is to switch slide assemblies between #3 (black plug) and #1 (kinda lean plug).

One of four things will happen:

a) #1 is black, #3 is OK (bad jet needle)
b) #3 is black, #1 is OK ((bad jet needle seat)
c) Both #1 & #3 are black (both jet needle & seat are bad)
d) Both #1 & #3 are OK (Full moon effect, call it lucky!!)
​

I'll post tonight on my progress.

Thanks,

mike

 

[Guest]

One of four things will happen:

a) #1 is black, #3 is OK (bad jet needle)
b) #3 is black, #1 is OK ((bad jet needle seat)
c) Both #1 & #3 are black (both jet needle & seat are bad)
d) Both #1 & #3 are OK (Full moon effect, call it lucky!!)
​

Actually, let me revise my predictions a bit:

a) #1 is black, #3 is OK (bad jet needle)
b) #3 is black, #1 is OK ((bad jet needle seat or something else)
c) Both #1 & #3 are black (bad jet needle & seat & maybe something else as well)
d) Both #1 & #3 are OK (Full moon effect, call it lucky!!)
​

 

[Guest]

Just weighing in - although I think you already checked it.

I had this headache ance, where the problem was a pilot jet not fully tightened down, allowing extra gas to get past.

 

[Guest]

I had this headache ance, where the problem was a pilot jet not fully tightened down, allowing extra gas to get past.

Wish it was that easy! I just replaced all the jets & made sure ALL were tight. thanks for the suggestion...

mike

 

[Guest]

Actually, let me revise my predictions a bit:

a) #1 is black, #3 is OK (bad jet needle)
b) #3 is black, #1 is OK ((bad jet needle seat or something else)
c) Both #1 & #3 are black (bad jet needle & seat & maybe something else as well)
d) Both #1 & #3 are OK (Full moon effect, call it lucky!!)
​

Ok then, after switching jet needles the result was:

b) #3 is black, #1 is OK (bad jet needle seat or something else.)


But the really good news is I MAY have found the something else.

What I noticed while putzing around was that the choke rail wasn't returning all the way when the choke lever was pushed closed. It was leaving all 4 choke plungers open a tiny bit. The cause was kinda strange - the choke cable "jacket" wasn't staying in the adjustment fitting located at the bracket attached to top of carb 3. This is the bracket where the cable part threads through a small dia tube, and then heads for the rail connection.

When the choke lever was pushed open, the jacket got pulled out of the fitting, & the edge of the jacket would hang up on the edge of the fitting. Then, when you pushed the choke lever closed, the cable was essentially shorter & wouldn't let the rail return all the way - wasn't open by much, but enough where the choke was still on a bit... Not sure if that was a constant or intermittent problem.

The next thing I discovered was all 4 of my exhaust flanges weren't really tightened down. I easily removed all 8 mounting bolts; brushed them all clean, applied a liberal amount of anti-seize, & then reinstalled them tighter.

I didn't have a chance to test ride the bike after fixing this stuff, but I'll be taking her to work in the morning so I'll know tomorrow...

Anyway, hope this does it!! If so, I still have to set the mix screws better & redo the sync.

All you guys are right - the basics have to be checked & double checked when an issue is driving you nuts.

thanks,

mike

 

[GSJim69]

I had a very similar problem on my bike after cleaning the carbs. The pilot jet that I previously could not get out had fallen out after I had installed the carbs and ran the engine.
Imagine my surprise when I pulled the fuel bowl off and saw the pilot jet, stripped screw slot and all, laying there.

 

[Guest]

still looking for the cause...

still looking for the cause...

Well, I got work this AM and just pulled the plug at lunch - STILL BLACK!!

I will say that the bike ran much better on the way in though; smoother with less vibration.

I'll fiddle some more tonight I guess, but I'm getting discouraged

 

[Guest]

I had a very similar problem on my bike after cleaning the carbs. The pilot jet that I previously could not get out had fallen out after I had installed the carbs and ran the engine.
Imagine my surprise when I pulled the fuel bowl off and saw the pilot jet, stripped screw slot and all, laying there.

Glad yours worked out - nice when you can see that "cause & effect" relationship so clearly!!

 

[Don-lo]

Dang, I thought the choke was a good possibility. I would still pull that plunger and inspect it...

 

[Guest]

I'm perplexed!!

 

[Guest]

OK, last update...

OK, last update...

Got home last night & the bike ran lousy all the way home. Feels like
a dropped cylinder; vibration, stumbles, sounded "ticky"...

Can't imagine what could have happened between the morning ride & the afternoon ride ? It just sat in the parking lot, looking pretty...

Once home, played with the mix screws a bit to optimize the idle - then went for ride. Still stumbly & the forever black #3 plug.

Getting to the end of the riding season here for me in NE (low 40's this morning) - I'm starting to think more & more about my real true love: skiing fresh powder in VT !!!

Besides, my 1100 is REALLY feeling lonely & neglected, I have to spend some time with her before she gets too mad...

Anyone want to buy a GS850GLZ ??

Frustrated,

mike

 

[49er]

Got home last night & the bike ran lousy all the way home. Feels like
a dropped cylinder; vibration, stumbles, sounded "ticky"...

Can't imagine what could have happened between the morning ride & the afternoon ride ? It just sat in the parking lot, looking pretty...

Once home, played with the mix screws a bit to optimize the idle - then went for ride. Still stumbly & the forever black #3 plug.

Getting to the end of the riding season here for me in NE (low 40's this morning) - I'm starting to think more & more about my real true love: skiing fresh powder in VT !!!

Besides, my 1100 is REALLY feeling lonely & neglected, I have to spend some time with her before she gets too mad...

Anyone want to buy a GS850GLZ ??

Frustrated,

mike

Mike, you've eliminated spark by a fairly thorough analysis, which really only leaves excess fuel or serious oil fouling of the plug. If it's an oil issue, you should be noticing the engine smoking on decel or even when reved into the upper rev range, with a need to top up your oil level on a monthly basis. If these symtoms aren't present, it leaves fuel delivery to that cylinder. IMO, you need to recheck the following areas.

1. Check that there is no partial restriction to the #3 carb inlet in the airbox.
2. You have eliminated a faulty needle valve/wrong float level by confirming the 5mm of fuel in each bowl.
3. You said that the problem is most obvious in the mid range of the rpm which probably equates to 1/2 to 3/4 throttle positions. This points to a problem with the needle jet or the jet needle on #3 carb. If a PO has swapped out these, you could have the wrong combination on that cylinder. It's about the only logical conclusion, going on the acccuracy of the information supplied!!

 

[Guest]

Thanks 49'er, I appreciate your thinkin' this through.

I have ordered one new jet needle & seat to replace the set in carb #3. I have to remove the carb rack from the bike to install 'em, so I'm inclined to just dip all 4 carb bodies as long as I have it off. I don't really want to, but I suppose it would be in my best interest to do so...

I may as well double check the valve clearances too, there was some carbon in the cylinders (based on looking in the plug holes) when i got this baby. I put a capfull of seafoam in the oil when I changed it out & ran about 150 miles that way - changed out that oil & filter and put fresh 10-40 dino in... The oil was very black & the bottom of the drain pan had quite a bit of organic particulate matter in it - carbon crud I assumed, no metal bits. I was wondering if the valves were really seated when i adjusted them the first time, but a compression test shows good compression.

Anyway, can't hurt to check them again, maybe a valve or 2 isn't opening??

Lots of rework staring at me at a time when the season is winding down, so maybe this will turn into a "next" year project.

Thanks,

mike

 

[KEITH KRAUSE]

Just wondering what the history is of the parts and the bike.
Did it run fine at one time and then start to have this trouble or did you inherit this problem?
Replacement carbs can be a lot of trouble due to neglect and/or poor servicing.
You still haven't tested it at specific throttle positions, chopped off, and read the plug to see any changes. It sounds like the jet needle circuit to me. If you swapped jet needles and saw no change, that suggests the needle jet could be worn.
It could also be a clogged primary air jet as I mentioned. You didn't say you proved it was OK/clear.
I'm also wondering how good the carb synch is. Have you proven vacuum is similar to the other 3? Have you also tried another plug?

 

[Guest]

Just wondering what the history is of the parts and the bike.
Did it run fine at one time and then start to have this trouble or did you inherit this problem?

Don't know any of the past history - bike was sitting (covered) for 15 years when I bought it. The guy I bought it from never ran it, just stored it for the last 3 of of the 15 years. Approx 7K on the ticker.

Replacement carbs can be a lot of trouble due to neglect and/or poor servicing.

Bike sat with gas in the tank/carbs for all that time - VERY YUCKY when I started cleaning the fuel system up. All stock parts, obvious I'm the first guy in there...

I've dipped/rebuilt 3 sets of CV carbs prior to this one, but still I know I may have not done a good enough job - each body sat 24 in my "old" can of Berryman's, then another 24 hrs in a "new" can of Berryman's. Tank's been POR'ed & a new petcock as well...

You still haven't tested it at specific throttle positions, chopped off, and read the plug to see any changes. It sounds like the jet needle circuit to me. If you swapped jet needles and saw no change, that suggests the needle jet could be worn.

True, I've not done that yet - I am planning to do so. I ordered one new jet needle & needle jet to replace the ones in#3, just as a last resort before tearing it all apart again.

It could also be a clogged primary air jet as I mentioned. You didn't say you proved it was OK/clear.

When I had it apart the other day I verified that passage was clear.

I'm also wondering how good the carb synch is. Have you proven vacuum is similar to the other 3?

I synced them using a Morgan Carbtune, 1 & 4 are equal, 2 & 3 are a little less. Haven't re-synced since I changed the mix screws settings, or swapped around the jet needle, but didn't "ungang" them or touch the sync adjustment screws...

Have you also tried another plug?

Yes. swapped between 3 & 4, and also used a brand new one - same result.

 

[Guest]

Happy update !!!

Happy update !!!

While the forum was down, I FINALLY fixed my carb problem that resulted in a fouled #3 plug, and made the engine run on 3 cylinders.

The problem turned out to be a badly worn needle-jet. I bought 4 new OEM ones and the all my problems vanished. In fact... this bike now runs excellent!!

I cut the "bad" needle-jet in half length-wise to inspect it: the corrosion on the inside diameter resulted in lots of voids that allowed fuel to bypass the jet needle and reach the outlet holes where it shouldn't have gotten to, thus dumping fuel into the carb and fouling the plug.

Although I inspected these needle-jets when I initially took the carbs apart, I guess I didn't really look inside them too hard. I may just start routinely replacing them on subsequent carb rebuilds.

I just re-sync'ed the carbs this evening and this bike is running very, very nicely!!! It's a shame the riding season is coming to an end here in NE, although it's been unseasonably warm lately .

Thanks for hanging around to hear me out.

 

[49er]

While the forum was down, I FINALLY fixed my carb problem that resulted in a fouled #3 plug, and made the engine run on 3 cylinders.

The problem turned out to be a badly worn needle-jet. I bought 4 new OEM ones and the all my problems vanished. In fact... this bike now runs excellent!!

I cut the "bad" needle-jet in half length-wise to inspect it: the corrosion on the inside diameter resulted in lots of voids that allowed fuel to bypass the jet needle and reach the outlet holes where it shouldn't have gotten to, thus dumping fuel into the carb and fouling the plug.

Although I inspected these needle-jets when I initially took the carbs apart, I guess I didn't really look inside them too hard. I may just start routinely replacing them on subsequent carb rebuilds.

I just re-sync'ed the carbs this evening and this bike is running very, very nicely!!! It's a shame the riding season is coming to an end here in NE, although it's been unseasonably warm lately .

Thanks for hanging around to hear me out.

Thanks for feeding back your results. Many don't have the manners to manage that part. Enjoy your riding, whats left of it.
Cheers.

 

[tfb]

Another excellent result!

Be sure to follow-up with a carb-synchronisation now that the dust has settled. I used to think that they were kind of optional until a plug-fouling problem was cured by a carb-sync...

 

[Guest]

Another excellent result!

Be sure to follow-up with a carb-synchronisation now that the dust has settled. I used to think that they were kind of optional until a plug-fouling problem was cured by a carb-sync...

Already done last night with my new Morgan Carbtune - great little instrument, easy to use & bullet-proof.

BTW - I plan on posting a pic of the ID of the "offending" needle-jet, to show the corrosion/cavitation that caused the problem. Good lesson to be learned here (don't let me near your carbs).

mike

 

[salty_monk]

Interesting... as they're brass I never thought it possible they could corrode & cause a problem like that!

Glad you fixed it