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  1. #1

    Default Priming System Operation

    I am trying to troubleshoot a flooding issue and am wondering how the electric priming system works. I have a 1988 20HP (J20ECCA)

    I have confirmed that the primer is not leaking fuel when not engaged. I pumped the fuel line bulb with the engine not running, nothing comes out of the primer. However when the engine is running, I do see fuel flowing through the primer lines. (I've put clear fuel lines on).

    It appears that the fuel is flowing from the line that goes from the bypass cover to the primer. What is the purpose of this line? Is it part of the recirculation system?

    My understanding is that the larger line that runs from the crankcase to the top of the manifold (#27 in the crankcase diagram) is the recirculation line.

  2. #2

    Default Re: Priming System Operation

    Quote Originally Posted by emilkob View Post
    I am trying to troubleshoot a flooding issue and am wondering how the electric priming system works. I have a 1988 20HP (J20ECCA)

    I have confirmed that the primer is not leaking fuel when not engaged. I pumped the fuel line bulb with the engine not running, nothing comes out of the primer. However when the engine is running, I do see fuel flowing through the primer lines. (I've put clear fuel lines on).

    It appears that the fuel is flowing from the line that goes from the bypass cover to the primer. What is the purpose of this line? Is it part of the recirculation system?

    My understanding is that the larger line that runs from the crankcase to the top of the manifold (#27 in the crankcase diagram) is the recirculation line.

    Bumping this to the top of the pile. Can someone help me understand?

  3. #3

    Default Re: Priming System Operation

    To clarify, I understand that this line primes the bypass when the primer is engaged. What I am seeing is fuel flow from the bypass back toward the primer when the engine is running. This fuel is then going into the carb primer port. Is this backflow normal (i.e. part of the recirculating system)?

  4. #4
    Join Date
    May 2015
    Posts
    2,648

    Default Re: Priming System Operation

    There are no recicirculation/bypass lines attached to the primer. The primer is a one way valve that operates off the key. The key energizes the valve to open it. When the motor is spinning and the primer is activated the fuel pump pushes fuel through the primer. I believe you have 3 primer lines 1 to the carb, one under the carb to the intake and one to the transfer port. These are 1 way lines only.

  5. #5
    Join Date
    Sep 2010
    Posts
    22,482

    Default Re: Priming System Operation

    What is your motor doing / not doing ?----How did you determine it might be flooding ?----The electric primer is a valve that opens when key is pushed in.-----When motor is cranking the fuel pump pushes fuel through the open valve.-----This fuel goes into the motor and bypasses the metering circuits in the carburetor.----They work very well indeed.----Used for 25 years on motors from 9.9 to 300 HP.----I think you are seeing fuel vapour coming from fuel in the primer lines between the primer and engine.----Simply because of low pressure on one end.
    Last edited by racerone; 07-25-2021 at 06:36 PM.

  6. #6

    Default Re: Priming System Operation

    Quote Originally Posted by racerone View Post
    What is your motor doing / not doing ?----How did you determine it might be flooding ?----The electric primer is a valve that opens when key is pushed in.-----When motor is cranking the fuel pump pushes fuel through the open valve.-----This fuel goes into the motor and bypasses the metering circuits in the carburetor.----They work very well indeed.----Used for 25 years on motors from 9.9 to 300 HP.----I think you are seeing fuel vapour coming from fuel in the primer lines between the primer and engine.----Simply because of low pressure on one end.
    Racerone,

    The engine would idle, but big down and die when I advanced the throttle. Plugs would be wet.

    In troubleshooting, I put clear fuel lines everywhere. Once I did so, I noticed two things:
    1) The back flow of fuel from the primer line between the bypass port and primer
    2) The slow idle adjust screw had no effect on the idle quality.

    I read that a compromised fuel pump diaphragm could pump fuel into the crankcase. I took the pump apart, didnít notice any obvious rip/tear, but did notice that the diaphragm appeared stretched/tired, and part of a gasket that extended into the pump has a tear.

    I bit the bullet and recently bought a new fuel pump. Now, I donít see the back flow, but the engine will start, then quickly begin to sneeze and die. My current assumptions:

    - New fuel pump did indeed stop pumping fuel into crankcase
    - Now that I donít have the back flow of fuel from crankcase to carb primer inlet the engine dies as I must have a clog in the carburator ( maybe a piece of the ripped fuel pump gasket).

    i wonít have a chance to pull the carb off and rebuild for awhile

    Am I on the right path? Any thoughts?

    Thanks!

  7. #7
    Join Date
    Sep 2010
    Posts
    22,482

    Default Re: Priming System Operation

    The low speed mixture might be too lean and that causes the sneeze.----Or throttle plate might be open a wee bit , or open to early and that stops the motor.----Trouble shooting is easy if you understand how these 2 strokes work.

  8. #8

    Default Re: Priming System Operation

    Quote Originally Posted by racerone View Post
    The low speed mixture might be too lean and that causes the sneeze.----Or throttle plate might be open a wee bit , or open to early and that stops the motor.----Trouble shooting is easy if you understand how these 2 strokes work.
    Thanks for the quick reply Racerone!

    After installing the new fuel pump, I set the low idle screw to 1-1/2 turns out from seat and tried different adjustments. I also followed the link and synch procedure from the service manual. I am assuming at this point that it is indeed a clogged carb. I ordered a rebuild kit, and will try that in about a week. Will update after I clean/rebuild the carb. My brother has an ultrasonic cleaner he uses on carbs on his Sprint cars, so working with him we'll be sure the carb is good and clean. Will remove all Welch plugs and the lead shot so we have full access to all chambers. If that doesn't work, we'll at least know the fuel pump and carb are not the issue. Stay turned.

  9. #9
    Join Date
    Apr 2010
    Posts
    5,263

    Default Re: Priming System Operation

    Edit.....

  10. #10

    Default Re: Priming System Operation

    Finally got back to the boat. Took the carb apart, didn’t see anything obvious. Instead of rebuilding, I simply used compressed air to blow through everything. Adjusted the float slightly. And went to put the carb back on the engine. Imagine that, I never had the carb gasket on the intake. Grabbed the carb gasket from the rebuild kit and remounted the carb. Engine never ran so well before. I’m assuming my original problem was a bad fuel pump dumping fuel in the crankcase.

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