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Dominick, Marine Mechanic
Category: Boat
Satisfied Customers: 1009
Experience:  25 Years Experience as Mechanic, 20 Yrs Boat Yard Owner/Mechanic, Factory Certified
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Have 1996 mercruiser 7.4 carbureted engine that starts great

Customer Question

Have 1996 mercruiser 7.4 carbureted engine that starts great and runs good to about 2200 rpm. Struggles to get above this level. If I back down near idle I can get it to 3000 rpm before it quickly falls back to 2000. New plugs and wires. Distributer, rotor, and igNition senso module were replaced last year. Cleaned air filter. Fuel seems ok. Changed fuel filter and did not see any water on dump. Two weeks ago engine was running at 2800 rpm so lost about 600 rpm. Last year could run 4500 rpm with same props.
Submitted: 4 months ago.
Category: Boat
Expert:  Tan replied 4 months ago.

Hello. My name is Tan.

This is symptoms of fuel starvation. We will need a vacuum gauge, brass tee and some fuel hose. Splice the tee into the fuel supply line to the engine. Connect the vacuum gauge to the tee. Now run the boat and monitor the gauge. If it exceeds 2" of vacuum then you have a fuel restriction. This cab clogging fuel pick up tube, kinked clogged fuel tank vent, bad anti siphon valve or failing fuel line.

Do this test and post back with findings.

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