1977 merc 85hp runs good for few mins then cuts out?

[rcam97]

My 1977 mercury 850 will run perfect as soon as you first crank it as long as you get up to good speed, but as soon as you slow down it will not speed back up, it will only idle around. It runs great until I slow down and then it will not speed back up at all it just bogs when I give it throttle. I have rebuilt carbs with new floats needles and seats and set the float height. The stator, trigger assembly, switchbox, and the internal wiring harness have all been replaced with new parts. The timing is also right.

Any ideas?
thanks

 

[Wingedwheel]

Re: 1977 merc 85hp runs good for few mins then cuts out?

Did you replace the fuel pump and lines? It does sound like a fuel issue. Is the choke working freely?

 

[rcam97]

Re: 1977 merc 85hp runs good for few mins then cuts out?

Sorry forgot to say that, yes I did change all of the fuel lines and rebuilt the fuel pump. Thanks for the quick reply.

 

[SeaKaye12]

Re: 1977 merc 85hp runs good for few mins then cuts out?

Do you think it could be heat related?

What if you speed up (from a cold start); then immediately slow down. Does it then refuse to speed up again? Or is it only after a more prolonged run?

Then I'd look at cooling, and/or look for binding in the linkage (throttle and spark advance linkages) that might be operating differently when hot.

Sounds like you've done most everything else....

I have the same engine...so I'm naturally interested in the outcome.

Chuck

 

[iryancooper]

Re: 1977 merc 85hp runs good for few mins then cuts out?

Gentlemen, just purchased a 1977 Galaxie (tx) with the 1977 850 Mercury doing the exact same thing. Had my dad and grandpa look at - they are both stumped. He said fuel pump - but seeing that you already did that, I'm guessing my doing that will yield no result. Would you mind reporting back as to what fixed it? As soon as I get back down to idle, she dies. However, mine does have a problem getting started. I have to prime it - so I might still have fuel pump issue. Let me know what you did and many thanks. -Ryan

 

[Chris1956]

Re: 1977 merc 85hp runs good for few mins then cuts out?

Ryan, You might start a new thread and tell us exactly your symptoms. Thos old motors had bad wiring, and if neglected, the carbs get dirty and the fuel pumps leak.