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CCKA Onan Twin Miller welder AEAD Engine Diagnosis

One exhaust manifold was cold. So removed plug wire from other cylinder and the cold cylinder would hit intermittently, just enough to keep the engine running.

Also switched around the plug wires and spark plugs to confirm was not an ignition issue. This is a horizontally opposed engine. When I had the cold plug out and hooked to the plug wire, it seemed to fire as expected, not intermittently

Over time fuel was entering the crankcase and when I had both plug wire back on eventually due to overfilling, oil would get to exhaust of good cylinder and smoke me out.

I plan to pull the head of the faulty cylinder, but wondering if anyone could provide some insight as to possible issue. I am assuming it is either the cylinder wall damaged, or a valve issue.

This was a recently purchased unit and appeared as if was out in the weather for a long time.
I guess I better take a compression reading of each cylinder first, and I also have another double coil that I could try to eliminate the possibility of the coil somehow misbehaving. The cold cylinder is the one with the longest plug wire.
The CCKA on my P&H welder behaved like that when I first got it. A new, very expensive, ignition coil fixed it.

There are lots of Onan experts on the Onan Generator forum.
Governor leaks. It is mounted on the intake near the cylinder which was cold.

Will figure out from parts diagram if there is supposed to be a o ring or gasket where it mounts (approximately 1/4" hole in manifold).

Detected it by squirting a bit of fuel on it and then cylinder lite up immediately.

attached a photograph of governor, easy to remove, two screws and a spring disconnect.



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A vacuum leak to that side would lean ot the mixture enough ti cause it to drop out intermittently.

Double ended coils are frequently used in four stroke applications where 2 cylinders fire on 360 degree intervals.. one side fires on an exhausting chamber while the other is approaching tdc compression stroke.

When there's lots of compression and a lean mix, the coil can exhibit propensity to short through its windings on one or the other end of the coil. This will allow one plug a nice spark, while the other will miss and foul.

Obviously you've found the culprit hee, congrats!!!


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It could be a vaccum-modulated dampener... to supress oscillation under light load... but regardless, a vacuum leak is a vacuum leak... is a vacuum leak.