2002 Sea Doo X20 computer issue?

[buck5476]

I have had my boat to two different mechanics and they are baffled. The engine runs but fluctuates between 8 and 18 degrees when they check the timing while it is running. Once it jumps up to 18 and comes back down the engine will stall. The computer reads that there are no codes. The boat has had the engine compression checked on all cylinders and all are good. One plug fouls constantly (Top right while standing in the boat looking down at the engine). I'd hate to have to throw $1,600 at a new computer if that isn't the issue but both mechanics have worked on these boats before. Is it my computer or do I need to take it to a third mechanic?