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  1. #1

    Default 15 hp lower cylinder not firing despite spark tester says OK.

    My 15E76R had been upgraded to a CDI ignition two years ago. Ran much better with the upgrade. The problem first arose recently when at WOT the engine suddenly bogged down and I limped back to the dock.

    When I found a wire disconnected to the coil half of the plug connecting to the power pack I thought “end of story.” So I replaced the coil with a used one I had on hand (having tried unsuccessfully to reconnect the loose wire to the plug). But that did not solve the issue much to my bewilderment.

    Earlier this year it already had a carburetor rebuild, new fuel pump, new fuel line and new tank not related to any problem at the time but as an update.

    With the current problem I replaced the fuel in the tank.

    Also checked compression of 110psi on both cylinders, good water flow and thermostat operation per the pyrometer, synced the cam follower and cam, spark plugs show wet with fuel without fouling, changed the spark plugs, rechecked for loose wires.

    So I am at a loss; but wondering if something has gone bad such as the stator?

    Any thoughts would be appreciated.


  2. #2

    Default Re: 15 hp lower cylinder not firing despite spark tester says OK.

    PS It starts and idles easily on just the top cylinder.

  3. #3
    Join Date
    Sep 2010
    Posts
    20,250

    Default Re: 15 hp lower cylinder not firing despite spark tester says OK.

    Perhaps a broken reed valve.

  4. #4

    Default Re: 15 hp lower cylinder not firing despite spark tester says OK.

    Thanks Racerone.
    Should I expect to have to pull the Powerhead to get to the reed plate?

  5. #5
    Join Date
    Apr 2010
    Posts
    4,901

    Default Re: 15 hp lower cylinder not firing despite spark tester says OK.

    Will your spark jump a 7/16 " open air gap on a spark tester ??

  6. #6
    Join Date
    Jun 2013
    Location
    Duluth Mn
    Posts
    3,193

    Default Re: 15 hp lower cylinder not firing despite spark tester says OK.

    Are you sure you can still call the CDI an "upgrade". What year components were installed, and were they new or used? To test Reed valve you can apply vacuum to carb port after you have removed air silencer. I have a fitting for this. Perhaps you can fabricate one yourself. Otherwise you will have to remove carb and inspect visually......perhaps even remove reed block.....need new gasket then.
    Last edited by timguy; 07-27-2020 at 12:40 PM. Reason: Add info

  7. #7

    Default Re: 15 hp lower cylinder not firing despite spark tester says OK.

    Quote Originally Posted by Boobie View Post
    Will your spark jump a 7/16 " open air gap on a spark tester ??
    I finally got an open air spark tester and it does NOT jump a 7/16” gap; only about half that gap.
    So where might that lead me next?

  8. #8
    Join Date
    May 2015
    Posts
    2,317

    Default Re: 15 hp lower cylinder not firing despite spark tester says OK.

    switch box or coil.

  9. #9

    Default Re: 15 hp lower cylinder not firing despite spark tester says OK.

    Quote Originally Posted by flyingscott View Post
    switch box or coil.
    Please tell me what a switch box is. Power pack?
    Thanks

  10. #10
    Join Date
    May 2015
    Posts
    2,317

    Default Re: 15 hp lower cylinder not firing despite spark tester says OK.

    Quote Originally Posted by Smute View Post
    Please tell me what a switch box is. Power pack?
    Thanks
    Go to www.cdielectronics.com they have the testing procedure for your ignition.

  11. #11
    Join Date
    Jun 2013
    Location
    Duluth Mn
    Posts
    3,193

    Default Re: 15 hp lower cylinder not firing despite spark tester says OK.

    Right, great, simple diagnostics there. A switch box is Mercury name for a power pack....in other words, one in the same. An electronic ignition should arc at least 7/16" in open air. A good standard magneto should go 3/8" minimum. Both use a capacitor or condenser to store voltage for a moment in time.

  12. #12

    Default Re: 15 hp lower cylinder not firing despite spark tester says OK.

    Thank you both very much!

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