Fouling Plug, one cylinder

[AB4D]

Hi. Recently, my father gave me his CA78, titled as a 69'. He purchased it used in 1977. It's probably been sitting for 10 years since it last ran before it was given to me. The odometer shows 3995. I've rebuilt the carb and petcock and got it running. When my father gave me the bike, he said the left side plug always fouls out after a while. Comparing the spark plugs, it seems to support that conclusion. That side sounds a little different when it fires and there is some rich smelling smoke from the exhaust. I ran a compression test, and it reads 140 psi for both cylinders. I suspect oil leakage around the valve guides for that cylinder, but I have very little experience working on Japanese motorcycle engines, to base any conclusion. I've built automotive engines and worked on small gas engines, but nothing Japanese.

Looking for some ideas from the resident experts.

Thanks, James.

[48lesco]

James - That's pretty low miles for a valve guide issue. I'd check the resistor cap on that side. Maybe cut a 1/4" off the wire and screw it back on. Make sure the valves are adjusted too. Doesn't sound like a fuel/air issue if the right side is running OK.
-48

[AB4D]

James - That's pretty low miles for a valve guide issue. I'd check the resistor cap on that side. Maybe cut a 1/4" off the wire and screw it back on. Make sure the valves are adjusted too. Doesn't sound like a fuel/air issue if the right side is running OK.
-48

Thanks, I will check the items you mentioned. Another member suggested a possible o-ring or head gasket issue could cause oil seepage into the combustion chamber. I am just getting started to determine how much work I need to perform. It's in fairly good shape for it's age and all the parts seem to be present, but it does have some issues.[/img]

[48lesco]

OK let us know... Rich-smelling smoke sounds like unburned fuel to me, not oil. Worn guides are rare on these bikes, and at 140 psi you don't have ring issues. Probably just not firing consistently on that side.