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Thread: 1972 50hp. Evinrude fuel delivery issue

  1. #21
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    Remove the plug screw and retest. It must vent in order for the diaphragm to flex.
    I'd rather be fishing.

  2. #22
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    That is a good point, however if I remove the screw which allows the hole to be open to the atmosphere I would think that it would try to suck air then and not be able to Pump Fuel? What are the odds in the possibility that even though fuel is going through the Reeds as it should that there could be a leak in the crankcase valve that is allowing to fuel to go down into the lower cylinder or possibly somewhere else instead of the combustion chamber? This weekend I plan on pulling the powerhead and checking the lower seal as well as the top.

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  3. #23
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    The diaphragm separates the fuel and pulse sides of the system. The only way air could enter the system with the plug removed is by passing through a tear in the diaphragm.
    If there was a leak between the two cylinders, neither would operate correctly. The more likely issue would be a bad top crankshaft seal or a failure of the crankcase to seal in the area of the top cylinder. The result would be that the top cylinder would be pulling unmetered air through the leak, a weak signal through the carb and have a very lean mixture reaching the combustion chamber.
    I'd rather be fishing.

  4. #24
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    Since the bottom cylinder is operating correctly, there is no need to pull the powerhead.
    I'd rather be fishing.

  5. #25
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    If I were to pull the flywheel stator and timer base and apply air pressure to the top cylinder and spray the seal with soap and water would that be able to tell me the seal is bad or is there another alternative.

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  6. #26
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    Pull flywheel and look for excessive amounts of oil residue around the seal.
    I'd rather be fishing.

  7. #27
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    I will definitely give that a shot this evening and get back to you.

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  8. #28
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    Just an update, this evening I took off the flywheel and attached the compression tester hose to my compressor and adjusted it to around 30 PSI. I sprayed soapy water around the top seal and I had no air bubbles. I also sprayed the area where the two halves of the block would bolt together I had no bubbles there either. I did notice that I was having air leakage coming through the reeds depending on the Piston position just a slight turn of the prop would stop air coming from the reeds. I had a good flow of air coming through the prop so I know the exhaust Port should be open. I would have to disconnect the hose to be able to rotate the prop enough to seal off the air coming through the exhaust. I attach the hose to the number 2 cylinder also and had the same results. Depending on what everyone thinks I plan to reassemble the flywheel and carburetors and spin the motor while leaving the spark plugs out and see if I have any fuel spraying out by doing the paper method on the motor.Name:  20200917_181550.jpg
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