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  1. #1
    Join Date
    Dec 2018
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    Scotland
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    Default Johnson 15hp four stroke wont start ( bad timing?? )

    Got an early Johnson four stroke 15hp off a mate.

    Not a bad looking engine but it refuses to start.

    It was one he bought but couldn't get running.

    All that it does is give the occasional big sneeze out the carb after pulling it.



    Here's what I've tried...

    1. Checked timing belt. pretty sure on these that the timing is Cam sprocket mark lined up with extrusion on pull start mount and the crank at the split on the port side ( 270 degrees if looking down from the pull start)

    Found it to be a tooth out so took belt off and refitted.

    2. Checked plug wires if they were the wrong way round. No sneeze out of carb but would not start.

    3. checked spark with plug out, definately there as its sneezing occasionally.

    Plug wires are in pretty bad shape so could do with replacing. Is there anything else I should be looking at? Could be a bent valve?

  2. #2
    Join Date
    Sep 2010
    Location
    ontario
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    16,239

    Default Re: Johnson 15hp four stroke wont start ( bad timing?? )

    Plugs both fire at the same time.----So plug wires can be reversed as it does not matter.-----Recheck the belt timing with a manual.

  3. #3
    Join Date
    Dec 2018
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    Scotland
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    Default Re: Johnson 15hp four stroke wont start ( bad timing?? )

    timing checked with manual and it is correct

  4. #4
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    Sep 2010
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    ontario
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    Default Re: Johnson 15hp four stroke wont start ( bad timing?? )

    Have you checked valve clearance ?-----Does spark jump a gap of 3/8" or more, yes or no ?------Ignition parts are big money items.

  5. #5
    Join Date
    Dec 2018
    Location
    Scotland
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    8

    Default Re: Johnson 15hp four stroke wont start ( bad timing?? )

    Quote Originally Posted by racerone View Post
    Have you checked valve clearance ?-----Does spark jump a gap of 3/8" or more, yes or no ?------Ignition parts are big money items.
    I'll need to get some feeler gauges for that. I know it has spark visually checked and with the sneeze.

    I'll invest in a compression tester too as I think that will where we go next.

    Cheers Racer

  6. #6

    Default Re: Johnson 15hp four stroke wont start ( bad timing?? )

    I honestly thought all johnsons timing work off the timer base that's slotted to the key on the crankshaft which position all the piston in the right firing order & timer base is also link to the accelerator linkage which tells it to increase or decrease the ignition.

  7. #7
    Join Date
    Dec 2018
    Location
    Scotland
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    8

    Default Re: Johnson 15hp four stroke wont start ( bad timing?? )

    Quote Originally Posted by fishhawk90 View Post
    I honestly thought all johnsons timing work off the timer base that's slotted to the key on the crankshaft which position all the piston in the right firing order & timer base is also link to the accelerator linkage which tells it to increase or decrease the ignition.
    I think thats the later 4 stroke models that have the linkage.

  8. #8
    Join Date
    Sep 2010
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    ontario
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    Default Re: Johnson 15hp four stroke wont start ( bad timing?? )

    Fishhawk-----What do you mean by ----"the timer base that's slotted to the key on the crankshaft "-------You have confused me with that statement.-------And on the 4 stroke motor in this thread both sparkplugs fire at the same time !

  9. #9

    Default Re: Johnson 15hp four stroke wont start ( bad timing?? )

    my mistake it does not have that slot, it's the flywheel. it's the accelerator linkage it uses for the ignition.

  10. #10
    Join Date
    Dec 2018
    Location
    Scotland
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    8

    Default Re: Johnson 15hp four stroke wont start ( bad timing?? )

    Valves lashed as per manual

    150 psi both cylinders


  11. #11
    Join Date
    Sep 2010
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    ontario
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    Default Re: Johnson 15hp four stroke wont start ( bad timing?? )

    Not sure why the question is not answered..-----Does spark jump a gap of 3/8" or more , yes or no ?

  12. #12
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    Dec 2018
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    Scotland
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    Default Re: Johnson 15hp four stroke wont start ( bad timing?? )

    how do I check that?

  13. #13
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    Sep 2010
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    ontario
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    Default Re: Johnson 15hp four stroke wont start ( bad timing?? )

    2 pieces of wire glued / stapled / taped on a piece of wood.-----3/8" gap between them.------One end grounded to the block.----Other end stuck into the plug boot.

  14. #14
    Join Date
    Dec 2018
    Location
    Scotland
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    Default Re: Johnson 15hp four stroke wont start ( bad timing?? )

    ok, thats a new one for me but I've got nothing to lose at this point.

    If it fails that I have a bad coil pack or leads

  15. #15
    Join Date
    Sep 2010
    Location
    ontario
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    Default Re: Johnson 15hp four stroke wont start ( bad timing?? )

    I learned how to test MAXIMUM magneto output about 50 years ago.---------I use a spark checker with 4 gaps adjustable from 5/16" to 1/2"--------Laying plugs on the block is not a proper test.

  16. #16
    Join Date
    Dec 2018
    Location
    Scotland
    Posts
    8

    Default Re: Johnson 15hp four stroke wont start ( bad timing?? )

    luckily I'm not that old

    I will try and produce something tonight!

  17. #17
    Join Date
    Nov 2005
    Location
    Mt. Zion, Illinois,
    Posts
    903

    Default Re: Johnson 15hp four stroke wont start ( bad timing?? )

    Quote Originally Posted by racerone View Post
    I use a spark checker with 4 gaps adjustable from 5/16" to 1/2"--------Laying plugs on the block is not a proper test.
    Exactly. When I'm testing spark I like to remove the plug so I can see if the charge reaches the plug. If you have a bad plug that can give you a false reading. A properly grounded air gap tester set a the correct gap will tell you exactly if you are getting good spark.

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