Motorcycle Repair: XJ650 fouling plugs, valve timing, traumatic event

Question
Hi Chris, I have a 1981 XJ650 that ran ok until I was hit by a car (on the right hand side) at low speed. Since then the spark plugs are fouling every 10 to 50km. It started with #3(from the left), but has moved on to all four, and gotten worse. The fouling is black and dry. The mechanics who looked at the gear box after the accident replaced 3L of oil into a 2L sump, which I thought may have been the cause, but draining the excess did nothing. It tends to occur when I am idling at lights, gets better at higher revs, but always results in plugs getting fouled. I have tried to make the mixture lean with the pilot screws, but this did nothing. The air filter is not brand new but far from dirty. Ive tested the compression, which is ok. Ive also tried hotter plugs to see if they could deal with it but no luck. The spark seems to be ok when I pull one out and rest it on the engine and start it up.

Answer
Hi Ben.

There are a number of things that can, and do, go wrong with an engine after a traumatic event (crash, lay-down, etc.).

In your case, start with the carb synch and ignition and valve timing.  Also check the manifold connections at both the engine and the carbs.  The shock of impact could have loosened them up a bit.  There is also the possibility of damage that intrudes on the airflow, like a small dent in the manifolds or possibly cracks in the manifolds as well.

Start with those and let me know what you find.

Good luck and ride safe.
FALCON