1977 85hp Evinrude---no power

[bmayhan]

Hello everyone I have been reading post here and found them very helpful. However I have yet to find a question similar to mine. I have a 1977 85 hp Evinrude on a 16 ft tri-hull boat. At times it will runs great but other times it seems like it is running at half power. Last time out we were headed across the lake at full throttle but it was only running about 15mph, then the motor took off and we jumped up to 35mph for about 200 yds. Then it acted like it cut out and we slowed back to 15mph, every once in awhile it will take off and run good. It is very inconsistant. I have changed all the plugs(old ones looked decent) the fuel line, bulb and both connectors, the fuel filter screen, and bought a new fuel tank. I checked all the plugs and they have decent fire, all 4 shot about the same spark. I am out of ideas and not really a machanic, so any suggestions would be appriciated Thanks

 

[wavrider]

Re: 1977 85hp Evinrude---no power

While you have it running on the muffs,

Take a insulated pair of pliers and pull the spark plug wires off by the boots and see if there is a change in rpm.

troubleshooting from the spark plug back. See which one makes a difference and troubleshoot that circuit

If all 4 wires make a difference then fuel related, carbs, weak fuel pump, vent in tank, garbage in jets,

 

[Faztbullet]

Re: 1977 85hp Evinrude---no power

Sounds like you have a float sticking shut or trash in high speed jets of your carbs.

 

[bmayhan]

Re: 1977 85hp Evinrude---no power

Thanks for the ideas I will try them out on muffs and see what happens. I have another question about the bulb on the fuel line.. How firm should it be?

 

[wavrider]

Re: 1977 85hp Evinrude---no power

When you first pump it up it should be firm.
After the engine starts running the fuel pump will draw fuel through the bulb and it will get soft, this is normal.

 

[bmayhan]

Re: 1977 85hp Evinrude---no power

Thanks 'wavrider' that is exactly what it does. I thought maybe it should stay firmer. But atleast now I am starting to eliminate possible problems.