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Charles, Marine Mechanic
Category: Boat
Satisfied Customers: 3309
Experience:  US Navy (Ret) Certified Mercury Marine Tech with over a decade of repair experience.
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I have a Yamaha 6H4 3cyl 2 cycle outboard with poor throttle

Customer Question

I have a Yamaha 6H4 3cyl 2 cycle outboard with poor throttle response at times. Recent history is 3 new spark plugs, 1 new ignition coil,removed and cleaned carbs. Went out for a test run this morning, and made multiple starts and had good acceleration. This afternoon the engine would stumble and die when advancing the the throttle.This is the second time this week of experiencing poor throttle response.
Submitted: 2 months ago.
Category: Boat
Expert:  Charles replied 2 months ago.

Hello, my name is***** will assist you.

Expert:  Charles replied 2 months ago.

Make sure that you are getting a good supply of fuel from the tank to the engine. If you have a separate fuel tank that you could run off of, and it ran better, you have an issue with either the hose to the engine or inside the boats fuel tank, If it runs the same, Make sure that the fuel filter is clean and there is no water in the fuel.

Customer: replied 2 months ago.
Took the boat to the dock the other day before receiving your message to do a test run. Engine would not accelerate under load,throttle was advanced to the point of almost having the engine stall and gave a shot of fuel down the throat of the carbs. Engine accelerated with full throttle control beyond the stall point. Repeated test 6 times with same results, opened all idle mixture screws an additional quarter turn and test, acceleration achieved. Acceleration test several times at the dock and open water. Have not returned to the water to reconfirmed results.
Expert:  Charles replied 2 months ago.

The base setting for the engine would be around 1 1/2 turns from a light seat on the mixture needles. Let me know how the next test goes.

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