Yamaha 70hp 2 stroke '89

[blairmcgrath]

I am a novice with outboards. My 89 70hp has alarm sounding, pisser has only steam coming out whilst under idle, hard throttle has water coming out like fire hose -but hot, and the problem wont let all cylinders fire (I assume is safety measure). Impella is sound. I dont know where my thermostat is, any suggestions please.

[jiggin joe]

Look here. I assume this is your model no.

Yamaha Outboard Parts 1989 70ETLF CYLINDER CRANKCASE Diagram

no 30 on diagram

[99yam40]

When was the last time the water pump was replaced?
Sounds like you need a pump kit and make sure the housing is not a problem while you are in there.
The water pump should be pushing water out the indicator hard even at idle, at least the newer ones do.

[blairmcgrath]

Have checked water pump housing and impella - all seem sound. My question now is really A)Does this model of Yamaha have a "de-rating" system - where if an imperfection exists somewhere, the motor cuts down to running less cylinders as a safety measure and/or B) Does the alarm itself have the ability to trigger any such "de-rating"??