Expert: Jeff Grigg - 1/5/2008

Question
 It sputters at 1/3 throttle only. Works fine at all other ranges.
I Sprayed the carbs, changed plugs, changed the gas with no luck.

Answer
Not sure what you mean by sprayed the carbs, Bob. If you mean you sprayed some carb cleaner into the throat of the carb, it really wouldn't do anything.
It sounds like you either have a partial restriction inside the carb, a small air leak or a mis-adjusted carb.
I would remove the carb, throughly clean the carb with spray carb cleaner, and reassemble using new gaskets. Pay particular attention to the smaller passages in the carb.
Set the idle mixture where it was previously and then turn the adjustment out 1/8 turn. Rune the engine.
You may have to richen the mixture even more. Do it 1/8 of a turn at a time, allowing about 15 seconds between turns.
Do your adjustments in the water, not a barrel or on the hose. You can do the adjustments with the boat on the trailer. Once it appears to be right run the boat off the trailer.
See if this doesn't help. If not post back and be sure to include the year or serial number of the engine.
Jeff