Johnson A-25, SN 46333 – Won’t turn over

[stanley]

The Boat House wrote:

• This reply was modified 3 years, 9 months ago by The Boat House.

In addition to what Tubs posted,there are marks on fly wheel and mag plate that must align for engine to be properly timed.

[joecb]

STOP , caution… just a word of warning when checking the spark on an opposed twin motor so as not to damage the ignition coil. These motors have what is known as an ungrounded coil. The circuit for the high voltage ( the coil secondary winding) is completer by way of each spark plug gap and the engine block. To help understand… lets say that when the high voltage is built up in the coil and is to be discharged to the spark plug (s) , it follows this path to make a complete circuit. From one end of the secondary coil winding >>> to one of the spark plug wires >>> jumps the spark plug gap >>> to the engine block>>> to the other spark plug BODY >>> jumps that gap >>> to the other wire >>> and finally back to the opposite end of the coil secondary winding. Excuse the unprofessional explanation , but that is how it works. The CAUTION… when checking the spark or pulling over the motor it is critically important the this complete circuit be maintained to prevent damage to the coil from internal high voltage discharge. For example, when checking the spark on one plug , be sure that the other spark plug wire is connected to either an installed plug or grounded to the engine. If one or both wire is not connected to ground, coil damage may ( will ?) occur..

Joe B

• This reply was modified 3 years, 8 months ago by joecb.

[HARRISON JACK]

Gentlemen,
Thanks for all your input, corrections and suggestions. Looks like a pretty steep learning curve me, but I love these old suckers!

I’m back, had a stroke in November and am just now getting back into my motors. Since my last posting, I purchased a compression gauge – only have 30psi. So, what’s my next step?

Please keep is simple, as stated I’m a real rookie.

Harrison

[HARRY D. NICHOLSON]

Low compression could be caused by stuck piston rings. No start could be caused by exhaust ports in cylinders clogged with carbon.

[The Boat House]

Glad to here of your great outcome. Medicine
has come a long way from the time when these
motors we play with were manufactured.
The beginning of this video will explain what
is meant by stuck rings.
Tubs
https://youtu.be/KjSPM6mp4eY

[stanley]

I’d pull the cylinders off and see what’s going on.

[2fast4me]

Welcome back indeed!

2Fast4Me

[JOHN HOLBIK]

Back in the day when we used heavy oil at 8 to 1 mix ratio the old motors fouled a spark plug on one cylinder many a time.We came home on one cylinder on many occasions I never heard of a coil failure on a Johnson A or any other opoosed two cylinder outboard due to one plug getting all the juice.To the best of my knowledge the coil will only builld up the required voltage to fire the plug.

[HARRY D. NICHOLSON]

A carbon-fouled spark plug is the same as a grounded spark plug wire, it won’t hurt the coil, but no external spark is produced by it to fire the cylinder. Same as a carbon-tracked distributor cap. It won’t spark properly but the voltage is still going someplace.

[JOHN HOLBIK]

Thanks for the explanation Harry makes total sense when I think about it.I guess I should have listened better to my father He said think before you talk or type in this instance.

[Author]

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