Hi All,

I am having a few issues with my 1987 90hp Yamaha alarm sounding at full throttle.

I can travel around at 4/5th throttle (50-55km) with no issues at all, as soon as a push the throttle that half inch further forward (60km) I travel for 100-200 meters, the alarm sounds and the motor enters safe mode (2000rpm). Alarm stays on for 20-40 seconds turns off and away I go again.

I have done a fair amount of research on the Yamaha forums and spoken to a few local mechanics who have all suggested the motor is getting too hot, I have already completed the following:

• Replaced impeller
• Removed the head and cleaned out water jackets (no obvious blockages)
• Replaced thermostat (old thermostat was modified to stay open)
• Replaced Pressure control valve grommet and spring (Valve itself was in good condition)
• Tested thermo switch assembly (heat alarm) triggering at 80-90 degrees Celsius.

All of the people I have spoken to have suggested the motor is overheating, the tell tale is strong and when the alarm sounds I have removed the cowling and can place my hand directly on the head and hold it there for 30 seconds without causing any damage which makes me think that it is not the motor overheating. I thought there was a possibility that the heat sensor was faulty but as mentioned above have already tested that.

The alarm is a strong solid continuous alarm, can it be something to do with oil, fuel etc???

Any help on things to try would be much appreciated, taking it to a mechanic at $90 per hour will add up way too fast.