[bulletbob]

First off, if it runs ok at 90% it probably is something minor,, Here's how I would proceed,,, Pull both spark plugs, and check the gap, the specs should be easy to find online.. I have fixed MANY running problems on OB motors by cleaning and regapping the plugs.. Might want to simply replace them... Make SURE that gap is correct, it really is critical on OB engines.
Make sure the gas is fresh, that might be the problem,,, Again, I have fixed many running problems with fresh gas.. if you put new gas, new plugs and it still won't run right at WOT, I would suspect a clogged main jet in the carb, but typically when they are clogged you will NOT get good performance at 90% throttle either...bob