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

[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.

[hikermikem]

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.

[hikermikem]

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

[hikermikem]

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!!)

[spchips]

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.

[hikermikem]

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

[hikermikem]

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.

[hikermikem]

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

[hikermikem]

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...

[chef1366]

I'm perplexed!!