You can try some "magic in a can" at this point. SeaFoam or any of the 2 stroke carb cleaners that go in the gas.
The SeaFoam will give the added bonus of removing some of the carbon from the cylinders/pistons.
Alternately, a spraycan of Merc's "Powertune" (about 5 bucks at a Merc dealer - just follow the directions on the can) may get rid of the cooties at this point.
If the quick "preventative" fixes don't work, then you need to chuck the 35 bucks for a Seloc's manual and troubleshoot.
Your symptom could be caused by one of a number of things not even related.
A "gag" at full throttle could be - dirty filter, dirty carb, stuck float, fuel pump diaphram on the way out, air in the fuel lines, crap in the gas tank, crap in the gas tank pick-up or even an ignition component developing a "glitch".
So start with the easy stuff first - maybe even throw in a new pair of sparkplugs if the current ones are more than 2 years old...
