1986 70hp Evinrude going to idle when full throttle

[afalkowsky]

Have a 1986 70hp Evinrude that will go to complete idle when full throttle. Will start and idle just fine, but after 5-10 minutes of running at top speed the engine will slow down to idle without me touching the handle. It doesn't completely stall out and will sometimes even throttle back up. This boat sat for quite a few years so I'm assuming it could be a number of things but want to know where I should start.

 

[grtomboy]

Some motors have a safety feature they refer to as "S.L.O.W" where an overheat of sorts protects the motor by slowing the RPMs. Do you have an alarm panel? Water pump still peeing?

 

[flyingscott]

Probably not the slow system. What is the compression? Do you have good spark? Have you changed the waterpump impeller? If compression and spark check good I would look at the fuel system pump and carbs.

 

[afalkowsky]

Compression seems fine, always pumps water ok. Have not changed the impeller or cleaned carbeurators yet

 

[mrcj001]

Sounds like a fuel delivery issue

 

[175se]

Had that issue with one awhile back, was a chunk of (god only knows what it was) blocking the fuel pickup in the tank at times when it was calling for fuel.You said it sat for a number of years,just a thought.