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Old 08 April 2015, 14:23   #1
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Yamaha 30 - No water being pumped.

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!
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Old 08 April 2015, 14:39   #2
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Is it being run with the water higher than the level of the impeller (remember, it's higher than the AV plate)
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Old 08 April 2015, 15:08   #3
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What does the thermostat do on this model?
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Old 08 April 2015, 15:35   #4
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Is it being run with the water higher than the level of the impeller (remember, it's higher than the AV plate)
Yes, it is above the impeller by a couple of inches.

I think tomorrow I'll get it on muffs and see if having some pressure behind it makes a difference.

Ultimately, the only way to check things may be to take off the cylinder head to get access to the water jacket.
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Old 08 April 2015, 17:08   #5
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Yes, it is above the impeller by a couple of inches.

I think tomorrow I'll get it on muffs and see if having some pressure behind it makes a difference.

Ultimately, the only way to check things may be to take off the cylinder head to get access to the water jacket.
Don't start that til you've ruled everything else out. You don't want to disturb it. I'd rather take a powerhead off an older motor than change the head gasket.

Get it to normal depth in water and try it again 1st.
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Old 08 April 2015, 17:14   #6
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My mariner 75 had a short (about 30mm) black plastic tube that went from the top of the pump housing to the connecting tube in the leg that was a poor fit and would miss align easily of the gearbox was not put on carefully. Result was little water made it from the pump to the head.no idea if the smaller engine is the same but it might be worth a look.

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Old 09 April 2015, 09:27   #7
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Thanks.

No joy with an increased depth of water.

I took off the powerhead and had a poke about in all the channels I could access and ran a bit of wire down the pipe between the powerhead and the impeller. Then off came the exhaust cover thingy and I gave a clean to every channel I could find.

Back together and it pumped like a good 'un.

Now the bl**dy carb pees fuel out of the overflow when the primer is pumped. The float must have stopped floating or the valve got stuck.

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Old 09 April 2015, 11:35   #8
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Thats not too major. You may even be able to shift the muck holding the float valve open by emptying the carb through the drain screw and pumping fresh fuel through.
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Old 09 April 2015, 12:46   #9
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Thats not too major. You may even be able to shift the muck holding the float valve open by emptying the carb through the drain screw and pumping fresh fuel through.
Swapped it with one from the dead Mariner I am cannibalizing.

I think that more thrust will result from the flow of water out of the tell-tale than from the prop - lets hope its going round the powerhead before it leaves the tell-tale at 200 mph...

Mixture and idle speed next!

Thank you.
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