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Thread: 1972 50hp. Evinrude fuel delivery issue

  1. #1
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    Default 1972 50hp. Evinrude fuel delivery issue

    The motor I have is a 50273C I am not getting fuel to the upper cylinder. I have checked for spark and it jumps a 7/16 gap with no problem. Compression is 115ish on both cylinders. When I rev the engine I can clearly see fuel spraying out of the venturi on the carburetor. When I place my hand over the top carburetor i have suction and fuel will pour out of the throat when I take my hand off. I put new plugs in the motor per specs and gapped at .40 when I removed the plugs I noticed the bottom plug is sooty being that both mixture screws are 1.5 turns out. The top plug is as clean as the day it was installed. I replaced the fuel pump as well but have to pump the bulb to keep the engine running. Does anyone have an idea what can cause this issue? The motor was given to me and has had this issue since I recieved it.

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  2. #2
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    Sounds like you have a reed valve that is not working.

  3. #3
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    Forgot to mention in my original post but I have a donor 1976 55 horsepower that I swaped Reeds from. I realize that the reeds are not new but they came from a running motor that had lost compression. Not sure what a brand new set of reeds should look like but I did not see a problem with the set that came out of my motor or the donor

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  4. #4
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    Is it possible that there can be a bad gasket in the crankcase halves that is allowing the fuel to be pulled down and drawn into the bottom cylinder? I stated before I can visually see fuel being drawn into the top carburetor from the Venturi. Also it seems as if the pulse is not working to operate the fuel pump so I have to do it by hand via the bulb
    The fuel pump I purchased was new but it had the vent hole in the back so I plugged it off with a screw.

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  5. #5
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    is the the fuel line and bulb new or used ???? could have a issue with them !!!!

    "What if you woke up today with only the things you thanked God for yesterday"
    "Life without God is like an unsharpened pencil - it has no point. "AMEN"

  6. #6
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    I am using a tank with fuel line and bulb from another motor. I have no issues with the other motor.

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  7. #7
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    This motor is a little before my time, but putting your hand over front of carb. pulls fuel thru venturi of the high speed jet. U said low idle jet needles are 1.5 turns out rite ? I'd suspect that idle jet in upper carb. Is clogged. Or u said new fuel pump rite ? Does single fuel line come off of pump then tees( 1 to bottom carb. 1 to top carb.) If so use a piece of clear hose on single hose from pump a see if theirs air bubbles in line. If so then air goes to top bowl. If no air bubbles, pull top carb. And check float drop ( that's normally a high speed issue) remove float , pour some gas in small container and see if float floats . could be a sinking float but that normally causes flooding. Just throwing out ideas.

  8. #8
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    And another thing u said bottom plug is soothed as in running real rich, could be bottom carb. float is bad and all fuel is being used on that carb. Will motor idle at all?

  9. #9
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    When I put my hand over the top carb for 3 to 5 secs and pull away quickly then fuel just pours out the front of it. When I reved the motor, i could clearly see fuel spraying to the back of the carburetor. The fuel was spraying from the Venturi or what you would call the emulsion tube. Regarding the fuel pump, it is has three ports at the bottom and one in the back that I plugged with a machine screw(I got the size from another thread). There is an inlet, a pulse and one that feeds the bottom carb. There is an outlet at the bottom carb that feeds fuel to the top carb so there is no tee. I tore down and rebuilt both carbs when I got the motor because the no fuel in cylinder was apparent when I first got it. Rebuilding the carburetors was the first thing that I did and had left the idle mixture screws out 1 and 1/2 turns each for the initial settings before putting it in the water.

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  10. #10
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    And yes the motor will idle as long as I am holding pressure on the primer bulb which means that the fuel pump is not working as it should. I do recall that when I first inspected the reeds it looked like there was a channel for the pulse vacuum tube feeding the fuel pump actually channeled up to the top cylinder and I think that's the reason why I'm having the fuel pump issue as well is because something is going wrong with the top cylinder.

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