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1975 25 hp johnson help plz?

D

dcurtin

New member
picked up a 1975 25hp johnson, was running good the bottom cylinder stopped firing, had the coil replaced and it ran good for two short trips, now bottom cylinder is not firing consistently, it runs good for a while then starts to run unsteady regardless of throttle position, fuel system checked out fine, carbs are good, compression is good. What could be the problem? mechanic says it may be the stader? not sure about the spelling. is it an easy fix and how can i test it? thanks Dan
 
Re: 75 johnson help plz?

ground is in same place as the original and the connection is tight, it's a new coil so i assume the wire is good, bolt is clean and unpainted.
 
Re: 75 johnson help plz?

Remove spark plugs. Rig up a spark tester whereas you can set a 1/4" gap. Crank the engine and observe the spark which should jump that 1/4" gap with a strong blue lightning like flame on both cylinders.... a real SNAP!

If the spark is weak, yellow, faint blue, etc on either cylinder, it could be due to dirty points, a leaking condenser, something of that nature.

There is a charge coil located under the flywheel that provides power to the two external coils. This could be looked upon as a "stator" BUT if this component was faulty, it should affect both external coils.

What spark plugs are you using and what is the gap setting? The recommended spark plug would be Champion J4C or J6C, set at .030. If you're using the J4C, try the J6C which is a slightly hotter plug which may provide improved performance.

Let us know what you find.
 
Re: 75 johnson help plz?

The plugs are the j6c type, I'll check things out as per your suggestions and let you know how it goes. thanks ALOT Dan
 
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