I'm with rollcaster, I'd do the cheap dumb stuff first. If there was any trash sucked into the carbs it could float free while at rest only to get sucked back up against a high speed jet when under power. If it's solid matter all the cleaners known to man wont help. The motor is 10 yrs plus old, wouldn't hurt to do the carbs. Merc carbs have the reputation of being finicky if you don't know them that well, best done by a reputable pro. Keep us posted please.

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Chairman Of The Bored
Prisoner of the White Lines on the Freeway
Fishin my life away.