1978 Mercury 7.5hp no power in forward

[sherlock]

5 mph max in forward, new impeller, carb kit and tune up, in reverse engine will rev up, in neutral engine will rev, in forward 10% rpm max. in a barrel forward will rev to max. short shaft on a 12ft aluminum with a 16 inch transom. any ideas

 

[CharlieB]

Re: 1978 Mercury 7.5hp no power in forward

Running in a barrel will not give near as much load as on the boat and in the water.

Two things will severely limit power, low fuel flow or a weak spark.

Check both. Disconnect the fuel line to the carb and crank the motor to see if you are getting a strong pulsed flow, if not, check the fuel pump diaphragm, alcohol in the fuel can cause hardening, restricting movement and flow.

Check spark using an adjustable spark gap tester set to at least 1/4 inch, if the ignition will not throw a hot blue arc, it needs attention as that will limit power.

Repost your results.

 

[Mi duckdown]

Re: 1978 Mercury 7.5hp no power in forward

check compression First