Ref; Force won't pump water at 2000 rpm's

[ralphhotdog]

98 Force 40 hp Yesterday I pulled out the thermostat and hung it in a pot of water with a thermometer. It opened at about 135 degrees. Then I back flushed it from the thermostst hole with the garden hose. After that I put an extention pipe in the thermostat hole and started the engine for a few seconds(I got good water volume out of it but not much preasure)So today I took the water jacket plug out of the cly. head and screwed in a water preasure gauge(What kind of preasure should I get?) and went to the river. At idoil I got a good spray from the exhaust port but no preasure reading on the gauge. At 2000 rpm's I got no spray and no preasure reading on the gauge. I reached back to the exhaust port with my hand and it feels like it is drawing vacume. After that I shut it down to let it cool while I gave it some thought. After cooling I started the engine and cranked it up to 3000 rpm's and covered the exhaust port with my hand and yes it is drawing in like a vacume then the engine starts to speed up and slow down on it's own so I backed it down to idoil a few seconds and shut it off. At idoil it runs as smooth as a 2 stroke could and any time during the process I can put my hand on the cyl head and count 7 seconds before I have to remove it. Any other ideas folks?

 

[captbob]

Re: Ref; Force won't pump water at 2000 rpm's

I am having the same problem with my 96’ Yamaha 115. I spent the whole weekend changing impellers, flushing, cleaning thermostats and taking the boat on and off the trailer. I removed the lower unit numerous times. I still have not fixed the problem. The next step is to put 2 new thermostats in, but I don’t think that is it. I can’t imagine where the blockage may be as I have flushed & back flushed and have great water flow then. Please let me know if you come up with a fix.