online vendors I've used and will use again (in order of personal preference):
iboats.com
ishopmarine.com
crowleymarine.com
marineengine.com
I would highly recommend getting yourself a service manual. It'll save you litterally $thousands over a couple-three years.
I don't know the '03 yammy in particular but here's some basics on outboard carburetors.
Outboards are particularly sensitive to dirty carbs, but they aren't that hard to clean or keep clean. They are surprisingly simple devices, unlike like the automotive carbs you used to see on cars.
Thing about aerosol carb cleaner is that, anything sprayed through the carb of a running engine goes right past the orfices and tiny passages that need cleaning straight through into the cylinders, where it does what its designed to do: strip oil off of metal surfaces.....not something you want in your combustion chamber.
I use chemtool B-12. soak all metal parts in it overnight, but be advised a lot of plastics will dissolve in it, and it's not so good for rubber, either.
There is probably a recommended special tool for removing the jets from the carb for cleaning, but if you spray aerosol carb cleaner liberally into every nook and cranny, and if they aren't too far gone, you can probably get it clean without taking the jets out. course there's always the chance that you'll have to go back and re-do 'em. I used my dremel to fabricate the tool for my evinrude, from a screwdriver. You'd need the manual for a description or picture of the yammy tool.
It's not really reasonable to expect an additive to clean a dirty carburetor, but there's a couple products that will keep 'em clean.
I add an ounce of seafoam per gallon of gas to my tanks, haven't had a problem since I started with that. Course if I let the motor sit for more than a couple months (rare), I usually clean the carbs just on general principle (that's how easy it is).
"Stabil" also comes highly recommended.
