1980's 40 HP Evinrude Troubles

[EyeNCrappieGuy]

Hey Gentlemen.

I have an older 40 HP Evinrude electric start tiller. It typically starts, trolls, and idles fine. My trouble comes when trying to run it wide open. It will sometimes only go about 1/2 throttle, even though you turn it wide open. After the throttle is half way open, and you continue turning, there is no noticeable difference in sound or speed. When happening, it won't even plane out. Even more mystifying is that one day it will run fine all day, and the next it will never make plane. Still other days it's mixed all day. This has been going on for a year or so and I'm ready to take care of it this spring!!

Does anybody have any ideas on what would cause and/or fix this type of a "high speed" trouble?

All I've done so far is replace the plugs and run some Amsoil fuel system cleaner through it.

Thanks in advance!

[eurolarva]

Remove both of the spark plugs and describe what the tips look like. Is one clean and the other dirty? If one is clean that unit cylinder will be the problem. Without further information it could be a fuel pump, dirty carbs a cylinder with no fire, a blown head gasket or a bad cylinder. Another thing you can try is choking the motor at WOT and see if that kills the motor or improves the performance. If it improves the performance you have a fuel related issue. The best thing to do is do a spark test and a compression test. These tests will tend to narrow down what is going wrong. Most cases it is a fuel problem like a dirty carb or a blown fuel pump diaphram.

[EyeNCrappieGuy]

OK, thanks!

One thing I forgot to mention, I don't have a choke (that I know of) but it does have an electric primer bulb....when it's acting up and I'm at WOT and keep pressing it repeatedly, I can reach "top speed" but typically as I stop jamming the primer, it coasts back to a fast troll.

So taking what you said, that would be pointing to some type of fuel system issue then. At least this is a starting point!

[eurolarva]

I am a force chrysler guy and will leave it to someone who knows evinrudes. My answer is pretty generic and I agree you have a problem with the fuel system which is good. Carb rebuilds, fuel pumps and such are pennies on the dollars compared to replacing electrical components. I am sure someone here will be able to help you that has evinrude experience. I would get a service manual if it were me. I personally like Clymor and factory manuals. Check out a larger public library and you can probably sign one out for three weeks. Good luck

[Valv]

Eurolarva found the problem. It's your carburators, they need rebuilt.

Your primer injects a squirt of gas past the carb to help cold starts, when you do this at WOT it means your jets are not allowing enough gas to go through or your floats won't allow much gas to come in.

Get 2 carb kits, follow instructions (if they have it, otherwise a good manual is a must), and it will solve your problem.

Bad jetting can also cause lean mixture on 1 or 2 cyls which can develop serious problem,s you have to fix this.

[EyeNCrappieGuy]

Thanks for the help on this one guys! Really appreciate it.

[ChuckN]

I've owned several OMC motors, including an '88 40 Johnson tiller, also a 60hp and that black "primer bulb" is actually an electric choke. Press and hold it for choke.

If you hit the choke and get higher RPMs I'm thinking a fuel delivery issue (fuel pump, hoses, etc) or dirty carbs, main jet particularily. Like other's have said...