Carbon Biuldup

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Brentf1965

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Sep 7, 2013
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16
I have a '79 Bobcat 720 with the Wisconsin engine. The #4 cylinder has 90 psi of compression but has a large buildup of carbon on the spark plug. I R/R the plug, operated the Bobcat for an hour, removed same plug and found it with carbon buildup again. The other cylinders have between 70-90 psi with no buildup. Any thoughts? Remember this is a '79 without a rebuild to my knowledge.
 

jerry

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May 3, 2007
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Do you have the service book? If I remember right in the 610 book it mentioned that there may be carbon buildup and gave a procedure for removing it.
 
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Brentf1965

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Sep 7, 2013
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Do you have the service book? If I remember right in the 610 book it mentioned that there may be carbon buildup and gave a procedure for removing it.
I don't have the service manual, but why only one cylinder with carbon buildup?
 

thynes

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Mar 16, 2014
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I don't have the service manual, but why only one cylinder with carbon buildup?
That cylinder is burning different than the other 3, for some reason. You have tried a new plug, so that is not it. How about the ignition to it? You can swap a plug wire and see if the problem follows the wire. You can do a tune up, wires, cap, rotor, points and see if that helps. You may also want to check the valve lash on that cylinder.
 

Tazza

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Dec 7, 2004
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That cylinder is burning different than the other 3, for some reason. You have tried a new plug, so that is not it. How about the ignition to it? You can swap a plug wire and see if the problem follows the wire. You can do a tune up, wires, cap, rotor, points and see if that helps. You may also want to check the valve lash on that cylinder.
It could be a lead i guess, not giving enough of a spark.
Possibly hotter plugs may help burn it all off.
 
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Brentf1965

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Sep 7, 2013
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Sure but lets be hopeful with a bad wire or cracked plug switch both first
I should have been more detailed with my first question. I actually changed out all plugs, all plug wires, points rotor, cap, and coil between checking the plugs the first time and the second time when I still found carbon on plug four.
 

antfarmer2

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Oct 28, 2013
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I should have been more detailed with my first question. I actually changed out all plugs, all plug wires, points rotor, cap, and coil between checking the plugs the first time and the second time when I still found carbon on plug four.
Can you ajust the valves on it
 

thynes

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Mar 16, 2014
Messages
71
Good Question. Does anybody have experience with VH4D Wisconsin?
I just rebuilt a VH4D this year. The valves can be adjusted. This youtube video shows some detail with the valves. http://www.youtube.com/watch?v=7E-osxPDcOk The intake valve is set to 0.008" and the exhaust to 0.016"
 

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