Problem is, it's not a Yamaha.
I'm really sorry for being a smart a$$. It was just too easy. :blush:
I know Mercs are great motors, and I know how frustrating it is when there's a hard-to-diagnose issue.
If the issue can be duplicated either on the lake or in a tank, I would think a trained mechanic (and his fancy computer-monitoring stuff) should be able to diagnose it fairly easy. With all the electronics and modules these days, it usually does take a computer to actually diagnose.
However if it is an intermittent problem, it can be a nightmare!
I hope you get it figured out and run it until the prop wears off ... and then go buy a Yamaha. :grin: