Vintage and Classic Hondas

Two cylinders puff white/gray smoke at idle, fouling plugs

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PG750K
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Two cylinders puff white/gray smoke at idle, fouling plugs

PG750K
Hey there  - new to the forum so let me know if this is out of place.

I am a new owner of an 81 CB750K that puts out a faint puff of white/gray smoke out of cylinders 3 and 4.  More smoke will come out when I rev it up.  

It runs and idles fine for a while, but inevitably it will foul the plugs.  I just pulled them and they were burnt to a crisp but did not have any oil or gas residue.

Could it be as simple as running too rich?  If it was a weak spark I would expect cylinders 1 and 2 to have problems too, right?
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Re: Two cylinders puff white/gray smoke at idle, fouling plugs

TOOLS1
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You need to run a compression test to determine if it is worn rings, or valves. If it was just two cylinders running rich, it would be black smoke.
TOOLS
Life is not about the number of breaths, you take, but the moments that take your breath away.
I don't have an anger problem. I have an idiot problem. Hank Hill
Never confuse education for intelligence.
Happiness is a belt fed weapon.
I just can't imagine what could go wrong.
No fire? No explosions? So whats the point of your story?
Those who are too smart to engage in politics are punished by being governed by those who are dumber. ~Plato
It couldn't be done, but the darn fool didn't know it, and did it anyway.
We all got problems. Ksharp
I like vintage bikes because they take me away from the clutter of technology that I work with everyday and back to a simpler time of mechanical elegance and simplicity.. "ninadm"
Darkwing Duck: The worst part of public transportation is the Public.
"That is awesome shit there" Re-Run
"Fear nothing, attack everything" Eric Berry
" Oh, you read that on the internet? Clearly it IS a massive problem. Of course it CAN’t be normal operation."

1976 CB 750-A X 2
1977 CB 750-A X 4
1977 CB 750-K
1976 CB 750 F
1981 CB 750
1966 Kawasaki SG 250
1981 KZ 750 LTD
1973 CB 350
1979 CM 185 Twinstar
1982 Honda XL 80
South of Eden (Kansas City MO)
PG750K
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Re: Two cylinders puff white/gray smoke at idle, fouling plugs

PG750K
Ran a compression test about two weeks ago (~20 miles) and everything checked out.
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Re: Two cylinders puff white/gray smoke at idle, fouling plugs

TOOLS1
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In that case, it sounds like a lean condition. You might have plugged jets.
TOOLS
Life is not about the number of breaths, you take, but the moments that take your breath away.
I don't have an anger problem. I have an idiot problem. Hank Hill
Never confuse education for intelligence.
Happiness is a belt fed weapon.
I just can't imagine what could go wrong.
No fire? No explosions? So whats the point of your story?
Those who are too smart to engage in politics are punished by being governed by those who are dumber. ~Plato
It couldn't be done, but the darn fool didn't know it, and did it anyway.
We all got problems. Ksharp
I like vintage bikes because they take me away from the clutter of technology that I work with everyday and back to a simpler time of mechanical elegance and simplicity.. "ninadm"
Darkwing Duck: The worst part of public transportation is the Public.
"That is awesome shit there" Re-Run
"Fear nothing, attack everything" Eric Berry
" Oh, you read that on the internet? Clearly it IS a massive problem. Of course it CAN’t be normal operation."

1976 CB 750-A X 2
1977 CB 750-A X 4
1977 CB 750-K
1976 CB 750 F
1981 CB 750
1966 Kawasaki SG 250
1981 KZ 750 LTD
1973 CB 350
1979 CM 185 Twinstar
1982 Honda XL 80
South of Eden (Kansas City MO)
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