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Tan
Tan, MerCruiser Certified Technician
Category: Boat
Satisfied Customers: 10620
Experience:  40 yrs. experience with complete engine repairs both inboard/outboard and MerCruiser Certified Technician.
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1994 7.4 merc bravo 3 power surges at high idle, boat runs

Customer Question

1994 7.4 merc bravo 3 power surges at high idle, boat runs fine at 40mph anything over that starts to bog down.
What I have done so far.
Removed anti siphon valves at top of both tanks.
Replaced cap, rotor, plugs and coil.
Replaced new fuel pump.
Put a fuel pressure guage on fuel line between carb and fuel pump.
Submitted: 3 months ago.
Category: Boat
Expert:  Jason replied 3 months ago.

Good morning, my name is ***** ***** am I speaking with?

All Mercruisers are cataloged by serial number, do you happen to have that number handy?

Customer: replied 3 months ago.
F117989
Expert:  Tan replied 3 months ago.

Hello. My name is Tan.

Have you tried adjusting the carburetor? Surging is usually a fuel related issue. Have you checked timing?

Customer: replied 3 months ago.
I am rebuilding the carb, it was pretty dirty.
Expert:  Tan replied 3 months ago.

It isn't unusual for an engine to have a surging issue from debris in the carburetor. The debris floats around in the bowl of the carb. The idle circuits are very small and this will cause surging. This can cause full throttle issues also. If you still have issue at full throttle then you need to run the engine on another fuel source or connect a vacuum gauge on the suction side of the fuel pump and run the boat. Watch the vacuum gauge it should never exceed 2" of vacuum. If it does then you have a fuel restriction in the boat side fuel system.

This can be debris in the tank clogging the screen on the end of the pick up tube, clogged or restricted vent or holes in the pick up tube. This should cover all the possibilities of the fuel system.

Post back with questions and findings.

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