Yamaha 3hp 2 stroke lacks power

[todwelsh]

My motor used to power my jonboat pretty well until it overheated one day (replaced water pump). I don't know if it was a result of the overheating but it just has not had the same full throttle performance since. It used to get the jonboat up on a plane but now it just barely pushes it.

Motor specs:

3MSHQ 6L5 1990 approx

I have cleaned the carb, fuel tank and lines. Idles well and playing with the choke at higher speeds doesn't help. The fuel pump diaphram looks a little worn so I will replace it. I don't think it is a fuel problem.

Compression: 90 psi (100 with a squirt of oil)

Checked the low and high speed pulser coils, charge coil, and ignition coils. Most were just slighlty higher than specs (5%), could be the meter.

I replaced the CDI module but that did not help. The wire to wire resistance measurements on the module don't match what the manual says but I am not using the same meter the book calls for.

Timing: I hooked up a timing light but the mark is not visible in the low or high speed window; though the timing does advance when the speed increases. The manual said to check the flywheel key but it is fine. It also said to check the CDI module if the key was OK. I don't know how else to check the CDI. Right now it seems timing could be the problem.

Any thoughts or personal experiences?

Thanks,

Tod
Little Mountain, SC

 

[BruceAML]

Re: Yamaha 3hp 2 stroke lacks power

You have a 1992 motor. Did you replace the spark plug and set the gap and torque the plug? The spark plug should be a NGK B6HS1. You should also add Yamaha RingFree to the fuel.

 

[todwelsh]

Re: Yamaha 3hp 2 stroke lacks power

I haven't replaced the plug, it still looks OK. That probably should have been the first thing I did. I am unfamilar with Ringfree, I will look into it.

Thanks,

Tod