1979 Johnson 15hp 2 stroke - starting problems/carb adjustments

[jsb5717]

I'm having problems with this motor. I've rebuilt the carb and can't find any adjustments other than the inlet float. The motor will start when cold, although it starts a little hard. Once warmed up it runs beautifully and strong. If I shut it off and try to restart it...nothing. It doesn't even try to fire. Once cooled off it will start with difficulty again.

Is there an adjustment I'm missing? Could the float be set incorrectly (too much fuel? not enough?)?

 

[raczekp1]

Re: Mid 70's Johnson 15hp 2 stroke - starting problems/carb adjustments

Re: Mid 70's Johnson 15hp 2 stroke - starting problems/carb adjustments

this starting problems when warms up can be becouse of:
1. if motor is1974-1977, weak condensers or coils,
2. if motor was overheated, head can be wraped and compresion is loosing, not sucking enough fuel.
i had wraped head in my9.9 1983.
when warms up it was very dificult to start.new head gasket and flattenig the head just help to solve the problem

 

[bktheking]

Re: 1979 Johnson 15hp 2 stroke - starting problems/carb adjustments

Your motor should have a needle sticking out the top of the carb , have you not adjusted it?

 

[jsb5717]

Re: 1979 Johnson 15hp 2 stroke - starting problems/carb adjustments

Is that the Low Idle adjustment? When I rebuilt the carb I seated the valve then backed it off 1 1/2 turns. I ran the motor and slightly adjusted it from there until the motor ran best. I'm not aware of any other needle...

 

[ONERCBOATER]

Re: 1979 Johnson 15hp 2 stroke - starting problems/carb adjustments

yes the needle on the top of the carb should be low speed needle, adjust it for best running (idle) when warm.... what ever adjustment takes to get there. Then put the hand adjuster (knob) back on it while warm to the center position. For cold start move it fully to the rich side and start engine, then as it warms and begins to act rich move it back to the center position, this will create a smooth running engine warm or cold.
your high speed is not adjustable except by changing jets or fuel level in carb (fuel level in carb should always be set to factory specs) the highspeed jet should be a prime focus on carb rebuild to know that it is in fact squeaky clean for sure, else it will run lean and cause problems.
Do you have a compression tester, if so thinking a cold and a warm compression test might be in order just as a baseline if nothing else.
Have you done a link and synch on the carb so that you know for a fact that the timing is correct? On my 83 15hp i set the timing just a tad more retarded to get a bit slower idle.
I agree on the possibility of a warped head, mine needed to be resurfaced and it made a huge difference. compression test may show this.
what spark plugs are you running in it and are they gapped correctly? what color are the electrodes when you look at em? tan, grey, black, oily, clean and shiny?
this is a bit of a long shot perhaps but a free test none the less.... does it make any difference if you pump the bulb? Thinking restart issue could also be leaky check valve or fitting allowing less fuel to be available... like I said... long shot but I would feel like I failed if i didn't include it.
Have you done a decarb? if so when was last one done?
I know the the link and synch, decarb, head flattening (if that is a word) and correct plugs, ea made a noticeable difference as i performed ea one.
If you have a spark tester make sure both hot and cold that the spark can jump 3/8" and strongly, if you don't have one no time like the present to pick one up or make one.
is it firing on both cylinders? you would be surprised to know just how good they can run on one cylinder (lol I found this out the hard way)

Keep working on it, you'll get it.

Sean