1985 Evinrude performance issue. No power at full throttle

[Darce Chandler]

I seem to have a bogging issue similar to some posted on this forum but nothing exact. A professional marine mechanic recently cleaned & rebuilt all carbs, replaced plugs and check each cylinder compression, all close to 130 each. I've replaced the fuel tank and fuel hose and bulb. After communicating my problem to the mechanic, he checked the engine again and reported he could not find any problems and that the engine runs fine!! I agree to a degree. The engine cranks and idles perfectly. It will even run at high revolution while the boat sitting still. (believe it could run forever like this). It will run well while moving up to 40 to 50% throttle. Beyond that it seems to starve for fuel while under a load. It doesn't die ---- just runs like an automobile with a potato stuck in the tail pipe! Tried the electric choke with no effect. Ensured air valve on tank was open properly. I would appreciate any help here. My wife and I are getting too old to keep pulling this thing out of the water. Thanks very much. 1985

 

[gm280]

:welcome: Darce Chandler.

First we would need to know what engine you have. I see it is a 1985 Evinrude, but what HP and model is it. Secondly is takes very little fuel to be able to revv out of gear. The fact that you can do that is basically a none issues. It sounds like a fuel delivery issue. But it could be that your advance ignition plate base may not be tracking the throttle position and therefore your ignition isn't advancing when you throttle up. Also up until you get to about where you are claiming the problem starts, is the idle and mid range sections of the carb(s). It is at that point where your high speed jet comes into paly. So even though you stated the card(s) were cleaned, it also sounds like the high speed carburetor circuit could have issues as well... And finally if your fuel pump can't keep up with the demand, you can have the same problems. So there are things you need to check or have checked by a competent OB engine mechanic... Post back what the results are... :JMHO!

 

[Darce Chandler]

Sorry!! The engine is 70 hp. on a pontoon boat
located 65 miles away in lake slip so can't get model no. right now.
Thanks for your reply.

 

[fireman57]

Is this a new engine to you? I mean did it run properly before? I have basically the same setup but can't get all the rpms I need out of it because the boat is too heavy. As for the bogging problem I go with the carbs. There is something in a high speed jet. I go through mine twice a summer because of the junky fuel they sell now. Ethanol seems to eat up fuel lines from the inside out. When the mechanic rebuilt the carbs ask him if he removed the welch plugs and cleaned the idle circuits. Also make sure that the timer base goes all the way to the rubber stop under the flywheel. If it doesn't then it is not advancing the timing like it should. You can check this with it not running. When it bogs have someone squeeze the primer bulb like a madman. If it picks up and goes then just replace your fuel pump.

 

[racerone]

If the motor has the wrong prop installed ( too high a pitch ) then revs will not come up.----There are simple ways to confirm operation of the motor.---Have it checked out with a test prop in a good sized water tank .---Or find a shop with a dynomometer to check the motor.---It is easy to ruin a fine motor with the wrong prop on it for the application !!!

 

[fireman57]

I'm down to a 9 pitch and can still only turn around 3500rpms. Not wanting to hijack this thread though.

 

[Darce Chandler]

Thanks for the timely and helpful responses. Little more info on questions asked. This outfit is a two owner. The boat, motor & trailer was purchased new 1985 or 86.
I bought it in 1995 and other than cosmetic upgrades to the boat and periodic normal maintenance (including 3-5 carb rebuilds), nothing has been added or changed. Performance has been great up until this year. When engine is running right, it pushes the boat well. Even now it runs like a scalded dog for about 15-20 seconds at full throttle-------thennnnnnnnnnnnnnnnn!! Thanks again.

 

[racerone]

Darce------Look into issues with fuel supply.----Run with a known to be good portable tank and hose.----Very little goes wrong with carburetors and not sure why they would have to be rebuilt that many times !!.

 

[Darce Chandler]

Thanks Racerone and all others responding. Your ideas and suggestions provides ammunition to solve my problem. Again thanks to a very knowledgable and intelligent group.