318 fuel/cylinder problem

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318 fuel/cylinder problem

Frank Gibbs Gentlemen: I have a 1983 318 that I just bought, real cheap, and was trying to get it to run smooth today. Adjusted carb, points, etc.. Then I pulled the spark plug wire from the left cylinder(looking at engine from drivers seat) and the tone of the engine did not change. The cylinder was not firing. I pulled the plug, grounded it against the motor and the plug is firing. Evidently, I am not getting any gas to the cylinder. Would a weak fuel pump contribute to this problem. Or, it is carbon build up that some solvent may cure. Or, do I have a major problem. Any help that anyone can give to me will be appreciated.
Dave Frank - When you pulled the plug, was it wet with fuel? If not, then either no fuel is getting to that cylinder, which seems odd if the other cylinder is firing. I'd try the same thing on the right cylinder to see if the engine then dies.

Also, check the oil to see if it has a fuel smell. It may be that fuel is bypassing the rings and getting into the oil. You should probably do a compression test on both cylinders. Optimum compression is 100 psi with no more than a 10 psi differential between cylinders.

The valves could be worn or out of adjustment spec. This could result in poor fuel combustion as well. - Dave

Frank Gibbs Dave: The plug was dry. When I pulled the other plug wire, the engine died. I have a compression tester but am unsure on how to check the compression on the Onan engine. Do I do it with both plugs out, or just the plug out of the hole that I am checking. I think I hold compression tester over hole and crank engine, is this not correct? I will check the oil, and the valves.
Tim Boisvert Frank,

Sounds like there may be a compression problem. You will need to measure it to be sure; pull both spark plugs, push the compression tested in the spark plug hole and hold it there so that it doesn't allow any air to escape while you crank the motor over.

If it is a compression issue, it could be as simple as adjusting the valve tappets. Worse case is that a valve seat came loose, fell out and trashed the block.

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