80's 60hp Evenrude slows near full throttle

[phillips407]

My motor starts and runs good until you reach a certain high speed, then it backs off and seems to try, but can't get on up to higher rpms/speed. When you back it off and increase speed again, it does the same thing every time. It recently had a tune-up and ran good at the shop, but now this. It has fresh fuel with proper mix. If it's something simple, I'd like to fix it, if not, I'll have to take it back in---a long way for me. Any thoughts will be appreciated.

 

[HighTrim]

Re: 80's 60hp Evenrude slows near full throttle

First off, what is your model number so we can verify a year.

I would start by testing spark and compression. Ensure that the spark will jump the 7/16 of an inch gap with a bright blue ZAP!! and the compression is equal across all cylinders (within 10 percent)and about 100 psi.

If compression and spark check out, it is time to look to fuel delivery. When were the carbs last rebuilt? Will spraying pre mix into the throats pick things up? What about pumping the primer bulb? Choking the motor?

Let us know what you find, including what RPM she is slowing at, and whether you have a built in fuel tank.

 

[flabum]

Re: 80's 60hp Evenrude slows near full throttle

Sounds a lot like either a fuel restriction ...... bad fuel lines, bulb , filters, vent or pump. Could also be clooged up carbs.

 

[tashasdaddy]

Re: 80's 60hp Evenrude slows near full throttle

sounds like a tank vent is clogged, is you primer bulb collasping? using a built in tank?

 

[phillips407]

Re: 80's 60hp Evenrude slows near full throttle

Checked fuel system--all o.k.--bulb does not collapse and pumping does not increase the speed. New fresh fuel. It will start and run on a good plane at 3/4 throttle with no problem-very smoothe. Then if I go to full throttle it will surge and back-off, surge and back-off--over and over--seems to be trying, but can't hold it. Any other thoughts? Thanks--Phillip