Re: 10 Horse Johnson
When there's no load on it, the single cylinder that's firing can easily turn the other dead piston and therefore rev up fine. But when it's loaded up, the single cylinder can't do the work to turn the dead piston and the prop. The ol' single cylinder firing trick will fool you every time! One reason why it's better to buy a used motor after a lake test and not a test on the muffs or running in a trashcan.
You might want to get yourself a cheap spark tester-- they're very helpful.
Good luck,
JBJ
