PC has it right. You are probably to lean on the high speed mixture. Also, I suspect you are trying to adjust the mixture on the beach. DON'T DO IT!!!!!!!!!! The engine has to sound rich at idle on the beach and that is where the throttle should stay, at IDLE. Adjusting the mixture is a trial and error process with the boat running under power in the water. Unless you know Nitro ENGINES, that run on Fuel (not "gas") it may be a frustrating task but the engine has to be under a load to adjust the mixture correctly. If anyone tells you differently, I suggest you turn and walk away.