Topic: Carbon fouled plug. What am I missing?? I GIVE!!!!

[Duke McDukiedook]

Clean that problem carb again if the wire/cap/plug check out to be good. Check all those three first.

[iron_worker]

I would be tempted to set your float level back to stock as Lucky suggested. Sounds like your bike is mostly stock so why not start with the stock settings?

IW

[TwoTired]

I expect #1 carb is not like the others.  Gonna have to look inside and compare to one that is working as expected.

Did the Slide needle jet fall out?

[mrrch]

Try swapping the sparkplug leads(#1 & #4) to see if the problem switches to the other cylinder. That will rule out the ignition if it doesn't.

[73CB500K2]

The most common run rich problem on these bikes is by far plugged up emulsifier tubes and by the way they are always over looked when doing a rebuild.

Did you check and clean the emulsifier tube ( aka main jet holder ) When bikes site for years they commonly rest on the side stand and the # 1 and 2 carbs get all gummed up because the fuel sits in those 2 carbs longer than in 3 and 4.

[scottly]

But whenever I have removed float bowls they never are more than 3/4 full.

Remove the float and put it down into your 3/4 full bowl, Lucky, and see how much the fuel level rises.

[grumpy]

I re-re-re-re-re cleaned all the brass incl the emulsifier, needle, needle holder (it was screwed all the way in BTW)
Re-re-re-re checked the float height.
Compared the float needle to the others and made sure it stopped the flow of fuel when it should.
Blew out the air screw path and meticulously turned it out to 1-1/8.
Hell, I even checked the bowl drain screws.

NOT ONE F'ING THING DIRTY, BENT, UNCLIPPED, MISMATCHED, ETC

NO F'ING CHANGE!!!!!!!!!!! STILL SOOTY!

 

Tomorrow I'll check sync again and swap the 1 & 4 plug wires.
I'll also pull a spare float out of the parts drawer and try that.

Then, I swear, it's M80s in the carb throats.

This is nuts.
I used to flippin' work fine!!


So its either:

Too much gas - been chasing that one
too little air - don't see how it could be
unequal vacuum - we'll see what the sync says
bad spark - maybe, we'll see tomorrow
alien brain probe - got my tinfoil hat, should be safe.

[scottly]

Re-re-re-re checked the float height.
Compared the float needle to the others and made sure it stopped the flow of fuel when it should.

Just to be perfectly clear, did you check the FUEL LEVEL with the CLEAR TUBE METHOD??? Did a NEW spark plug instantly turn sooty?

[grumpy]

Just to be perfectly clear, did you check the FUEL LEVEL with the CLEAR TUBE METHOD??? Did a NEW spark plug instantly turn sooty?

Yep and yep.

Well, not a NEW plug but an almost new one from the other side of the bike.

[scottly]

Inspect the post the main jet screws into. Look for cracks or severe corrosion that might allow fuel to bypass the jet. Compare the post to one of the good carbs; I recall an instance on here where a member had one carb with an odd length post. If I recall correctly, he had to set that float at a different height to compensate. The only other thing I can think of is some air passage in the carb body is blocked. I still stand behind the statement that poor ignition does not cause sooty plugs.

[BAchvytrk]

is it possible there is a choke issue on carb number 1? choke stuck on at least part way? I only say this as i had this issue with a set of yamaha carbs recently.

[lucky]

Try swapping the sparkplug leads(#1 & #4) to see if the problem switches to the other cylinder. That will rule out the ignition if it doesn't.

Excellent idea.

[lucky]

Inspect the post the main jet screws into. Look for cracks or severe corrosion that might allow fuel to bypass the jet. Compare the post to one of the good carbs; I recall an instance on here where a member had one carb with an odd length post. If I recall correctly, he had to set that float at a different height to compensate. The only other thing I can think of is some air passage in the carb body is blocked. I still stand behind the statement that poor ignition does not cause sooty plugs.

I agree completely.

[iron_worker]

Just read about someone who put one slide in upside down .... Just checkin? lol

IW

[longshanks]

Grumpy,

I had the same problem forever on my bike until I swapped out the carb bodies. It turned out there was too much between the slide and the carb body bore, which was on number one especially. I mentioned to another member to check the gap with a feeler gauge but you could use a dial gauge too. Of if you have the carbs off you can compare by inserting both of you fingers on either opening of the carb and wiggle the slide back and try to feel if there is a discernible difference. Not very scientific, but it might help you!   

[grumpy]

... turned out there was too much between the slide and the carb body bore, which was on number one especially.

Not sure I'm following... so the bore for the slide was too big & it sat loose?

Mine is #1, too BTW

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Wife's got me doing stuff to get ready for her sisters coming over tonight. Might not be able to get to this til tomorrow 

[longshanks]

... turned out there was too much between the slide and the carb body bore, which was on number one especially.


Not sure I'm following... so the bore for the slide was too big & it sat loose?

Mine is #1, too BTW

No I mean the bore in the carb body is bigger than the slide. I have a theory that the tolerances can get loose over time.

[grumpy]

F*** it!

Redid everything.
I mean everything.
For like the 8th time.

Jets, synch, fuel, floats, plug wires, cap, carb boots, the post the main jet screws into, the emulsion tubes...

still there.
Points to it being a problem with the body itself, like TT and Longshanks say.
But I just can NOT understand how it worked OK in the past. Something changed.
Maybe something cracked and I just can't see it?
 
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I installed my other rack of carbs. Works fine. Plugs are great all the way across.

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I need to leave it alone for a while, now. Let the carb cleaner & fuel fumes clear from my head.
I'll measure the bores, and other dimensions when my patience has returned.

[lucky]

<<====   750k3

standard airbox, K&N filter, cleaned and oiled
120 mains

How much oil on the filter? What weight?

[grumpy]

Official K&N oil.
Whatever weight that is.

http://www.knfilters.com/search/product.aspx?Prod=99-0504

[scottly]

<<====   750k3

standard airbox, K&N filter, cleaned and oiled
120 mains

How much oil on the filter? What weight?

What difference would it make how much or what weight? If it were a restrictive filter, it would affect all four cylinders, not just one. Besides, he switched the carb rack and it fixed it.

[lucky]

I have run into some motorcycle problems and they seemed to have no answer. But the answer is to take a break. Then start from the beginning one more time and be very careful and take your time. It never fails to find an answer.

Was this bike running good previously?

[lucky]

<<====   750k3

standard airbox, K&N filter, cleaned and oiled
120 mains

I have seen owners apply oil that was too heavy, and it settled to the bottom of the paper filter and clogged one or more carbs with very thick oil droplets.


How much oil on the filter? What weight?

What difference would it make how much or what weight? If it were a restrictive filter, it would affect all four cylinders, not just one. Besides, he switched the carb rack and it fixed it.

[scottly]

It's not a paper filter, Lucky. Paper filters don't get oiled. If you did oil one, it would certainly cause problems, but it would affect all four cylinders.

[madScientist]

Total long shot but could the oil be blowing by the rings on that cylinder?