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Whitecap36
Whitecap36, Marine Technician
Category: Boat
Satisfied Customers: 1545
Experience:  28 years Certified Marine Technician and past FL State Certified teaching degree
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1970 or 71 mercury 200 20 hp. After replacing impeller and

Customer Question

1970 or 71 mercury 200 20 hp. After replacing impeller and old fuel, motor starts and runs great but does not attain full speed. Also engine stops at full throttle under load as if flooding out. Any ideas??
Submitted: 6 years ago.
Category: Boat
Expert:  Whitecap36 replied 6 years ago.
Hello, I'm Mike.
The first thing to try and figure out is whether the problem is fuel or ign related.
You will need a can of carb cleaner and a timing light to perform these tests.
While engine is running at the problem spot spray carb cleaner into carb and see if it picks up if not run your timing light on each spark plug and watch the strobe light for an ign miss.
If the engine picks up with the cleaner then try squeezing primer bulb to see if it helps. If it does you will need to look at the fuel pick up,hose and pump. If not you need to inspect the carb and repair.
If the ign shows a miss start with a new set of spark plugs.
Customer: replied 6 years ago.
squeezing bulb does not help still stalls at full throttle under load. Has new plugs, new carberator, new coils. Is there any possibility that a change of props could raise rpms and effect top end timing ???
Expert:  Whitecap36 replied 6 years ago.

Without results from the tests I mentioned I'm not really sure.

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