yamaha loss of power

[sbs80]

I have a 1986 70hp yamaha. It has been running great until recently. After engine heats up 5-10 minutes, it will not turn up over 2000 RPM. When engine is shut off for 1 minute it will turn up to 3000 once and then only 2000. There seems to be a strong stream of water from the pee hole. It seems to smoke a little when this problem arises.

 

[ianyoung77]

Re: yamaha loss of power

sbs,<br /><br />Does it run smoothly at 2000rpm or rough. Does it stall at all?<br /><br />Ian

 

[rcgt78]

Re: yamaha loss of power

Hi,<br /><br />A strong stream of water from the pee hole doesn't tell the hole truth about proper cooling!<br /><br />Do you know what service have been done to the engine over the years. List them up if you can. It will be easier for people on the forum to help with the troubleshooting.<br /><br />How is it with the thermostat? Check if it opens at the correct temperature.<br /><br />Robbi

 

[sbs80]

Re: yamaha loss of power

Checked impeller, soft, pliable and well-greased. The water pump was rebuilt 8 years ago. When trying to go over 2000, it goes blub, blub, blub, blub. Not much water coming out of upper vent at idle. I looked at thermostat and cleaned with vinegar. It opens, but not sure at what temperature. After cleaning thermostat, engine ran fine for 25 minutes, and then begin to have same problem. I feel it is an overheat problem. The engine runs smooth at 2000 rpm or under and doesn't stall and idles smoothly. We have just rebuilt carburators.

 

[ianyoung77]

Re: yamaha loss of power

sbs,<br /><br />I had an overheat problem and replaced my impellor. The problem was solved, however, if I gave you the old impellor you would think it new. It was soft and pliable. How old is your impellor?<br /><br />Ian

 

[sbs80]

Re: yamaha loss of power

I have an entire kit for the water pump. Should I just replace the impeller or should I replace all the plates and gaskets?

 

[Lasse Lehtonen]

Re: yamaha loss of power

If the impellor seems to be like new and there is a strong (straight) stream of water coming out of the pee hole the problem is not the impeller I think your problem is that thermostat, take the thermostat out of there and block the hole where the thermostat has been so at water cant flood out of that hole and run then with higher rpm.If it runs over that 2000 rpm when warmed change the thermostat.Try also is the water coming out of the pee-hole hot.

 

[ianyoung77]

Re: yamaha loss of power

sbs,<br /><br />I agree with Robbi, the strong stream is not the whole story. Change the impellor and make a judgement on whether to change the gaskets depending upon the condition the old ones.<br /><br />How long do you take to flush? Have you ever used a flush addative to try cleaning the cooling system?<br /><br />Ian

 

[sbs80]

Re: yamaha loss of power

IT HAS BEEN ATLEAST 10 YEARS SINCE A FLUSH.<br />WHAT ABOUT A REVERSE FLUSH AND HOW WOULD I DO IT?<br />I AM GOING TO TRY TAKING THE T-STAT OUT COMPLETELY AND REPLACE THE T-STAT HOUSING AND SEE IF IT HAPPENS AGAIN .IF IT DOES I WILL REBUILD THE WATER PUMP.<br />WHAT ARE YOUR THOUGHTS?

 

[ianyoung77]

Re: yamaha loss of power

sbs,<br /><br />I have never done the thermostat job. I know the water pump is easy and would probably start there since I know it worked for me<br /><br />Ian

 

[sbs80]

Re: yamaha loss of power

ALL FIXED!<br />THANKS FOR ALL YOUR HELP!<br />I REBUILT THE ENTIRE WATER PUMP AND THAT SEEMED TO DO IT.<br />THANKS AGAIN.