"but it still stalls if I really throttle it down. "
I remember the ads in the back of comic books
and magazines "Make good money
in your spare time! Repair lawn mowers and outboard
engines!" and from what I've met and heard, a lot of the folks in the business got started that way and haven't gotten any better over the years. Or, they've figured out that folks who can't figure out how to store their lawnmower over the winter are easy prey.
Unless you can find an outboard
shop with really golden recommendations, I'd suggest getting the shop manual and spending a weekend tearing it down yourself. Outboards aren't all THAT complicated, they're nowhere near as delicate as pocketwatches, and I'd guess you'll save a fast $200-500 by DIYing the overhaul
Then maybe get a set of waterwings and strap 'em onto the engine