Runs great, then at full speed motor loses power and shuts off...can anyone help?

[abesz]

1985 Evinrude 150 HP V6, when running at full speed the motor will make a racket noise and then slowly decrease in power(would be fully planed out and running for quite a distance). Once the motor kills, sometimes I can start it right of way and then sometimes it acts as if its froze up(then after a minute or two will start). Yesterday, this all happened again on the water and now seems as if I have lost power all together(in the past when this would happen, I would restart the motor and would run like nothing happened). Just wondering what could be the issue, thanks...

 

[Daviet]

Re: Runs great, then at full speed motor loses power and shuts off...can anyone help?

Is it overheating, have you checked the temp horn, does it work? Have you checked the compression?

 

[daselbee]

Re: Runs great, then at full speed motor loses power and shuts off...can anyone help?

Blew it up, man. Running lean, overheating and then the piston swells in the cylinder, causing it to shut down. Just a few mins, piston cools enough to allow the starter to turn it over again.

You will find seriously degraded compressions, and you will eventually be replacing/rebuilding the powerhead.

Very sorry to hear this...