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Fuel problem - Johnson 4.5 HP

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FishyBC

Contributing Member
I have a 1981 Johnson 4.5hp short shaft motor that I'm trying to get ready for fishing season this year.
I have gone through it and have one thing left not working properly. I discovered that it is not getting fuel to the carb. I replaced the fuel lines and rebuilt the fuel pump but it still isn't getting fuel to the carb.

If I pump the ball on the fuel line, fuel does pass through to the carb. I tested the fuel pump doing the blow test as it says on Leeroy's fuel pump rebuilding page and it works exactly the way he says it should.

I tried with everything back hooked up pull starting the motor with the fuel line off the carb. Should fuel squirt out each time I pull the pull cord ?
 
racerone said:
Yes , fuel should squirt out when motor is turning.
Click to expand...

Thanks Raceone.
So I've seen that it could be the fuel pump or leaks in the lines. I ran a different motor on the tank and hose with no issue last week and I'm pretty confident that the lines are tight. What else could it be ?
 
Those fuel pumps can be tricky to get correct. The pulse comes into the pump in the center hole between the two mounting screws did you put a new gasket and slowly tighten it down a little at a time nice and even. I agree pull the plug on the bottom of the float bowl and see if fuel flows nice and easy just put a little dish under the carb to catch the fuel?
 
FishyBC said:
Thanks Raceone.
So I've seen that it could be the fuel pump or leaks in the lines. I ran a different motor on the tank and hose with no issue last week and I'm pretty confident that the lines are tight. What else could it be ?
Click to expand...

So that carb I do not believe has a drain at least that I can see. I assume it would be on the bowl ?
I've removed and am soaking and cleaning the carb. I'll put it back together and see if that helps.
After removing the carb if I prime the bulb fuel shoots out.

When I used a bottle with a fuel line attached and held it above the motor so it was gravity feed it seems to work OK but the carb had some stuff in it so we'll see if this helps.

I'll report back this weekend.
 
So I think the issue might be with the pin that holds the float on the carb. It was difficult to get back in when I put it back together and I don't think it allows the float to drop when the fuel in the bowl is gone. When I pump the primer bulb periodically it runs great. It's like that plastic pin got swollen or something and now it's to big.
I'll see if I have another one around that fits. I'm guessing the float needs to drop to let the fuel pump know to pump in fuel ? Just a guess but I'll try it tonight and report back.
 
So I did replace the pin and the float moves freely with the new pin. I fired it up but it was still starving for fuel so I did some more reading and it talked about air getting into the system so I made sure all of the connections were tight
- On the fuel hose feeding the motor itself
- From the fuel fitting where the fuel hose and tank connect to the fuel pump
- From the fuel pump to the carb.

I also realized that I had not installed the gasket (spacer) that goes between the powerhead and the fuel pump. Still not sure what it does or if it makes a difference.

One of those two adjustments made the difference. It runs fine now and is getting plenty of fuel.
Thanks again for the advice.
 
That is not a spacer.---------It is a gasket that prevent the pressure pulse from leaking away.--------------The pump is operated by pressure pulses from the crankcase.
 
There would be my obvious issue. Thank you for the explaination. Not sure why I didn't put it back on the first time.....
Much appreciated.
 
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