Yamaha 90 2-stroke advice

[Observer]

I have re-commissioned the engine myself after an 18 months layoff. Got the engine started and all seemed well. However, after 5-10 minutes running (using earmuffs water supply) the engiine overheat alarm sounded. There was a steady stream of water from the tell-tale outlet all the time it was running.

Is this a symptom that will not appear with the boat in the water or is it something else? Any suggestions where I should look next?

[MikeCC]

Some older model Yamahas need the whole leg to be immersed up to the cavitation plate for correct water intake. ie you may need to run it in a tub rather than with muffs.

That's not definitive and there may be other issues!

[spartacus]

When was the impeller last changed? If it's been laid-up for some time, the blades on the impeller may be compressed - and not pumping water as efficiently as you'd expect. For piece of mind - I'd replace, after all it's only a £20 component - if you fit yourself.

[Observer]

Originally Posted by spartacus

When was the impeller last changed? If it's been laid-up for some time, the blades on the impeller may be compressed - and not pumping water as efficiently as you'd expect. For piece of mind - I'd replace, after all it's only a £20 component - if you fit yourself.

I checked the impeller and it seemed in good nick - the vanes were supple and all intact. I did plan to replace it but couldn't work out how to get it off the driveshaft so left it as it seemed okay.

If it was the impeller, would there still be good flow from the telltale? I assumed not, or does water pressure when using earmuffs give a flow from the telltale even if the pump's not working?

I have another problem though. Launched on the Thames today for trial and the engine wouldn't go into gear (the throttle lever moved but there was no drive at the prop). Could I have re-assembled the gearcase wrongly?

[Louise]

Originally Posted by Observer

I checked the impeller and it seemed in good nick - the vanes were supple and all intact. I did plan to replace it but couldn't work out how to get it off the driveshaft so left it as it seemed okay.

We experienced a similar problem some time ago with our Yammie although we were underway at the time. There was a steady tell tale stream while the overheat alarm was going off (3 times). It was the impeller that needed replacing and my other half did a step-by-step guide to replacing the impeller. HTH.

[Richard B]

Originally Posted by Observer

I checked the impeller and it seemed in good nick - the vanes were supple and all intact. I did plan to replace it but couldn't work out how to get it off the driveshaft so left it as it seemed okay.

Uh? How did you inspect it without removing it?

Originally Posted by Observer

the engine wouldn't go into gear (the throttle lever moved but there was no drive at the prop). Could I have re-assembled the gearcase wrongly?

Most likely you haven't lined up the gear linkage.

[Observer]

Originally Posted by Richard B

Uh? How did you inspect it without removing it?

I was able to lever up the impeller housing to reveal and inspect the impeller, which was stuck fast on the drive shaft. I didn't want to cut it off or use a lot of force to lever it up for fear of damaging the gasket, which it's sitting on. So I replaced the housing over the top of the impeller without disturbing it.

Originally Posted by Richard B

Most likely you haven't lined up the gear linkage.

Dead right - doh! Dragged the boat up to a service agent this morning and it took him all of two seconds to diagnose the problem.

He also reckons there's probably nothing to worry about with the overheat. He said running for 15 minutes (which I did) on earmuffs may easily trigger the alarm because insufficient volume of cooling water from a hose.

Thanks for responses everyone.