Carbon Biuldup

[Brentf1965]

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]

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.

 

[Brentf1965]

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]

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]

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.

 

[TriHonu]

It could be a lead i guess, not giving enough of a spark.
Possibly hotter plugs may help burn it all off.

Couldn't it also be oil rings failing?

 

[antfarmer2]

Couldn't it also be oil rings failing?

Sure but lets be hopeful with a bad wire or cracked plug switch both first

 

[Brentf1965]

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]

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

 

[Brentf1965]

Can you ajust the valves on it

Good Question. Does anybody have experience with VH4D Wisconsin?

 

[thynes]

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"