1972 Evinrude 50 HP 2 stroke fuel delivery issue.

Sink/Swim

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Hello, I have a fuel delivery issue with my 1972 Evinrude 50 h.p. She fires right up and runs strong, but after a few minutes of running she dies. The bulb is soft so I pump it up again and can hear the fuel filling the carbs. She will fire right up again and run a few minutes then die over and over again? I can pump the bulb while the motor is running to keep fuel going to the carbs and she will stay running.

History
I had a blown reed valve last season so I replaced both upper and lower reeds. I also did carb kits. Compression is 140 psi (top) and 145 psi (bottom)

What I have replaced with NEW parts... fuel line, bulb, fuel tank (new fuel), fuel pump, all lines to/from fuel pump and lines to carbs.

I replaced the fuel line that feeds fuel from the top carb to the bottom with a clear line and can see it sucking air after a 20 seconds or so of running. There is no fuel leaking from any lines or connections as well as the new fuel pump.

So my thoughts are, New fuel pump is bad? Something wrong with the exhaust vacuum from the crank case that makes the fuel pump pulsate to deliver fuel?

There is some water mixing with the gear oil so I will be replacing the seals, water pump etc.. Not sure if that would have anything to do with the fuel issue.

Any advice is appreciated!
 

Bosunsmate

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Re: 1972 Evinrude 50 HP 2 stroke fuel delivery issue.

Does the fuel bulb hold firm with engine off, ie is it getting air into it or is it able to hold firm?
Did you check the crankcase hole was clear before installing new pump?
 

Daviet

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Re: 1972 Evinrude 50 HP 2 stroke fuel delivery issue.

Will the engine continue to run if you keep squeezing the primer bulb?
Have you checked the fuel pump pressure and flow?
It wouldn't be the first time a new part was defective.
 

Sink/Swim

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Re: 1972 Evinrude 50 HP 2 stroke fuel delivery issue.

Yes the fuel bulb does stay firm with the engine off. I made sure the crank case vacuum fittings were clear when installing the new fuel pump as well as the intake manifold.

Yes the engine will run constantly if the fuel bulb is squeezed while the engine is running. If the bulb is not squeezed every 10-20 seconds I can see the fuel level drop in the clear line that feeds fuel from the top carb to the bottom carb.
 

kenmyfam

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Re: 1972 Evinrude 50 HP 2 stroke fuel delivery issue.

Check the pump output.
 

Bosunsmate

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Re: 1972 Evinrude 50 HP 2 stroke fuel delivery issue.

Unless your top carb is flooding it sounds like your fuel pump aint working right. But keeping your bulb firm indicates your top carb isnt flooding.
Disconnect your fuel pump from the engine and check you feel the fuel pump pulse from the crankcase, if so then time to look at how you put the pump together or if its faulty
 

Sink/Swim

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Re: 1972 Evinrude 50 HP 2 stroke fuel delivery issue.

Disconnected the vacuum line running to the crank case from the fuel pump and put a balloon on the line to see if there was a pulsating motion. The air was sucked out of the balloon and didn't fill up at all. The vac line seems to just suck in air instead of pulse.
 
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Bosunsmate

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Re: 1972 Evinrude 50 HP 2 stroke fuel delivery issue.

I suppose you dont have a vacuum guage on that?
What brand pump did you get?
 

Sink/Swim

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Re: 1972 Evinrude 50 HP 2 stroke fuel delivery issue.

No there is no vacuum guage on this motor. The brand of the new fuel pump is BRP evinrude Johnson genuine parts. Part # 0438559.
 

Bosunsmate

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Re: 1972 Evinrude 50 HP 2 stroke fuel delivery issue.

You could put a clear line from pump to top carb and see if that has air bubbles coming into it, it shouldnt after you have it running and the bulb was pumped firm
 

Sink/Swim

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Re: 1972 Evinrude 50 HP 2 stroke fuel delivery issue.

I will pick up some clear 3/4 fuel line tomorrow and let you know what I find. Thanks for the quick help and suggestions!
 

kenmyfam

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Re: 1972 Evinrude 50 HP 2 stroke fuel delivery issue.

So is there any output from the pump...... bubbles or not ??
Temp hose into a bowl or similar on output side of pump.
Strong continuous spurts = pump OK
Strong spurts tapering off as it continues = failing pump
Weak stream or dribbles or nothing = failed pump
 

peter wickham

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Re: 1972 Evinrude 50 HP 2 stroke fuel delivery issue.

A friend with a similar problem found water in carbys. A 40 hp would only run on quarter throttle until fuel bowl bulb was squeezed. He was going to replace fuel pump etc. but the problem was cured by loosening the carby fuel bowl and then pumping fuel through by the fuel bulb. I didnt see him do this but the problem is solved. He got the advice from an outboard dealer friend of his. I was involved in helping him diagnose it. I suppose pumping the bulb with the bowl loose would flush the water out. he had been running the motor with no fuel filter. hope this helps.
 

Sink/Swim

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Re: 1972 Evinrude 50 HP 2 stroke fuel delivery issue.

Thank you all for the suggestions!
I will test the fuel output line with a clear hose to see if there are air bubbles going from the pump to the top carb. It will be later this afternoon when I get off work. I will also disconnect the output fuel line from the carb and check the fuel flow (while motor is running) I don't think there would be any water in the carbs. I just rebuilt them and have a new fuel tank, fresh gas, all new lines. But I will be stripping the motor down soon if I cant find the issue externally.

I still find it strange the balloon I attached to the vacuum line that is supposed to operate the fuel pump deflated while the motor was running instead of pulsating?

Any suggestions are welcome!
I am determined to figure this out.
Thanks everyone!
 

racerone

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Re: 1972 Evinrude 50 HP 2 stroke fuel delivery issue.

Pump is operated by a pressure pulse in the crankcase when piston is coming down in the cylinder.---When piston is going up the reed valves may open and there will only be a slight vacuum pulse.-Perhaps there is an issue with lower crank seal.
 

Sink/Swim

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Re: 1972 Evinrude 50 HP 2 stroke fuel delivery issue.

I attached the clear fuel line from the fuel pump to the top carb. Pumped the bulb up and started the motor. The clear line running from the top carb to the bottom sucked air in after the usual 30 seconds. And the line from the pump also had air coming from the fuel pump. I squeezed the bulb and put fuel in both lines while running. And the line from the fuel pump stayed full and the line to the bottom carb had air. But this time the motor didn't seem to want to die in the normal 2-3 minutes without the bulb being squeezed. I turned the motor off after about 5 minutes for fear of running the motor with no fuel going to the lower cylinder.
 

Sink/Swim

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Re: 1972 Evinrude 50 HP 2 stroke fuel delivery issue.

I just disconnected the vac line from the crankcase and was able to easily make the fuel pump "pump" fuel through the clear lines by blowing short breaths into the vac line going to the pump. So I feel the new pump is good. I'm just not getting the pulsating air in the vac line to operate the fuel pump?
 
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Bosunsmate

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Re: 1972 Evinrude 50 HP 2 stroke fuel delivery issue.

Fill both carbs up, start the motor, prime the bulb tight and then do a drop test on both cylinders- ie pulling the plug for the top cylinder, seeing if it will run and then doing that to the other cylinder
 

Bosunsmate

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Re: 1972 Evinrude 50 HP 2 stroke fuel delivery issue.

By the way wheres the pulse line come from to go to the pump on that motor? Post a photo if you arent able to describe it really well
 

Sink/Swim

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Re: 1972 Evinrude 50 HP 2 stroke fuel delivery issue.

fuelvac (800x404).jpg The vac line is the lower black hose. I will perform the drop test this afternoon and let you know what I find.
 
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