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Spark plug gap almoat closed and covered in oil.
97 FXDWG
Bikes been sitting for 3 or 4 weeks while I was trying to figure out why it wasnt starting. Ignition sensor was melted. I replaced it with oem and made sure timing was exactly the same. Took it for a 20 min ride, after some terrible sputtering, backfire without touching the throttle, and terrible engine shaking, I came home pulled the plugs and this is what I see. Rear plug smashed almost to closed gap after being at .40 before the ride.
*I did a compression test last week and got 97psi on the front cylinder (went up to 120 when about a teaspoon oil was added) rear was 110 & 115. Oil had no effect on rear cylinder compression readings
Possibly excessive carbon on the piston causing the plug issue. You could have a broken oil ring or the ring gaps somehow managed to align themselves. Maybe a leaking valve guide as well. I would do a leak down test which might help to isolate the cause of the oil in the combustion chamber.
How long have you owned the bike? Have you ever replaced the plugs before? I ask because if the previous owner did engine work, ie high dome pistons, stroked etc the plugs may be wrong or even need to be indexed based on the piston.
If you've had it for a while and have changed the plugs before then all bets are off. Put a bore scope in the plug hole and see what's going on in there. As another posted said, may need to pull the head.
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Spark plug oily as hell
