This engine is driving me mad (well, certainly making me very depressed).
Its an early 90's Yamaha 30 of the '689' type common with the Mariner-badged version. Two cylinder, single carb two-stroke.
This morning I replaced the impeller and it pumped water like a fire-hose, coming out of the tell-tale on the powerhead, the low speed exhaust and the tell-tale in the mid section.
Having switched the engine off I started it again and no water anywhere...
It is being run in a dustbin with the water above the level of the anti-ventilation plate.
Troubleshooting so far...
- The impeller is definitely fixed to the shaft by the woodruff key
- The impeller vanes are bent in the correct direction (they point away from the direction of rotation).
- With the lower-unit removed, a hose-pipe applied to the water riser tube in the mid-section results in water coming out where it should
- With the thermostat cover off and thermostat removed, water poured into the holes in the casting appears where it should
- Water poured into the impeller housing appears out of the inlet grilles in the lower unit
- The seal between the impeller housing and the riser tube isn't a very tight fit but seems waterproof and is intact
- Starting the engine briefly results in exhaust fumes coming out of the (removed) thermostat housing
- Fitted the lower unit from a Mariner 30 that I had lying around
- Put it in gear to verify the shaft is turning
Everything seems to be as would be expected but the powerhead remains uncooled.
The water is either not being pumped, there is a massive leak somewhere or there is a blockage preventing its circulation.
Any suggestions for further troubleshooting?
Can the function of the impeller be checked with it fitted in the lower-unit and the lower-unit off the engine? The diameter of the shaft is greater than the capacity of any drill I own.
Can the riser tube be pulled out of the power head (and if so, can I refit it!)?
This has been sooooooo close to going on eBay a couple of times before but the whole engine / boat / trailer / kit shebang may well be listed soon. What a stupid past-time!