Evinrude 1983 35hp Fuel Pump Issues

[Stephen Fournier]

I completely rebuilt a 1983 Evinrude 35 hp motor and runs great.
The only puzzling issue I have is fuel starvation at WOT between 4500-4800 RPM and the engine starts surging.
The surging can be eliminated by squeezing the fuel line bulb.
I have thoroughly went through all other possibilities of the cause, timing etc.
After some research I noticed that there are two types of fuel pumps for this motor, one vacuum and two vacuum connections.
Does anyone know if Evinrude made this change due to fuel starvation issues with this motor?

[fleetwin]

I’m not sure I understand what you are referring to about the fuel pumps… I will have to look at a parts book, but I have never heard of an issue like this on the 1983 models. Perhaps there is something else causing the lack of fuel flow… Air leak, restriction in lines/tank, etc. Did you have the high speed jet out of the bowl, did you clean it with solvent? Sometimes the fixed jets get just a tiny bit of crud growth around the inner diameter, but everything “looks OK” when you pass light through the jet…Try cleaning it with a solvent soaked pipe cleaner.. The other thing to make sure of is that the jet is threaded into the bowl completely….If the jet backs out slightly, it will restrict fuel flow…

[fleetwin]

OK, I see that the part number for the pump has superceded several times. But there is still only one vacuum/pressure port, and this is on the back of the pump through the hole in the intake bypass cover… Does the pump look to have been replaced? There were problems with the “umbrella valve” pumps used around 1990…The little umbrella valves in the fuel pump would crumble and the pieces would get lodged in the carb….

This engine has the “economizer linkage”, correct? This adjustment is often confusing and set up improperly. Does your carb throttle shaft have a stop/roll pin that prevents it from going past WOT position and actually closing down again? If not, perhaps you have the economizer linkage set improperly causing the carb butterfly to go past WOT/horizontal position causing the engine to slow down/surge at WOT.

Tell us more about what you repaired/rebulit on this engine…

[frankr]

Stephen Fournier wrote:

I completely rebuilt a 1983 Evinrude 35 hp motor and runs great.
The only puzzling issue I have is fuel starvation at WOT between 4500-4800 RPM and the engine starts surging.
The surging can be eliminated by squeezing the fuel line bulb.
I have thoroughly went through all other possibilities of the cause, timing etc.
After some research I noticed that there are two types of fuel pumps for this motor, one vacuum and two vacuum connections.
Does anyone know if Evinrude made this change due to fuel starvation issues with this motor?

So, how about the pump you are dealing with on your motor? Does it have “one or two vacuum connections”?

[Stephen Fournier]

This motor was completely disassembled, stripped, block rebored to 20-thousands over, new pistons and rings (150 PSI both pistons) , new bearings, water pump replaced, new thermostat, new powerpacks and CDI, resurfaced head, primed and painted. I mounted it on a 1980 14.5-foot Alumacraft with a jackplate and actually use it for bass fishing here in Florida. I used an OMC repair manual and followed the step-by-step instructions to rebuild the motor. My only disappointment is the surging issue at WOT and I am determined to resolve it.

[Stephen Fournier]

Only one vacuum connection.

[fleetwin]

OK, did you check the economizer linkage adjustment?
The best way to determine if indeed you have a fuel pump/supply issue it to connect a fuel pressure gage and clear hose from the fuel pump outlet to the carburetor. Keep in mind that low pressure readings could be due to an air leak, or restriction in the fuel inlet side. Did you try a different fuel tank?
I remember you mentioning that pumping the fuel bulb seemed to resolve the issue, which most likely indicates some sort of fuel delivery issue. But, a misadjusted economizer linkage or a bit of residue build up in the high speed jet might present similar symptoms…

• This reply was modified 4 years, 4 months ago by fleetwin.

[Stephen Fournier]

Thank you for the response.
I’m going through a few changes and will report my results in a week, or so.

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