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1965 Johnson 18 hp starting problem

T

Tincan46

New member
Engine will start and run for a few seconds then die. If left sitting for several minutes it will do the same thing. I took it to a “mechanic” who had it for 2 months and didn’t get it running. I have good spark both cylinders,checked with spark tool. Carb was rebuilt with OMC kit with no change. Swapped carb and still had same problem. Was told by a friend I may have a leak in exhaust bypass gasket or head gasket allowing a small amount of water into cylinder extinguishing flame. Was also told might be lower crank seal which they said was carbon and sometimes cracks. Would leaking seals cause this situation. Just need idea where to start looking for a solution. Not a mechanic, but pretty handy and not afraid to tackle anything. Thanks in advance for any suggestions no matter how far in left field they may be.
 
Basic trouble-shooting procedure is to check compression first... then check the spark as mentioned above.

As above... Remove the flywheel to check the coils etc.

Note that checking spark simply by having the spark plug removed and hooked up to the plug wire is a waste of time.

The spark (on that magneto model) must be checked by having it jump a 1/4" "Air Gap" with a strong blue lightning like flame... a real SNAP! Does it?
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(Spark Tester - Home Made)
(J. Reeves)

You can use a medium size philips screwdriver (#2 I believe) inserted into the spark plug boot spring connector, then hold the screwdriver shank approximately 1/4" to 3/8" away from the block to check the spark or build the following:

A spark tester can be made with a piece of 1x4 or 1x6, drive a few finishing nails through it, then bend the pointed ends at a right angle. You can then adjust the gap by simply twisting the nail(s). Solder a spark plug wire to one which you can connect to the spark plug boots, and a ground wire of some kind to the other to connect to the powerhead somewhere. Use small alligator clips on the other end of the wires to connect to ground and to the spark plug connector that exists inside of the rubber plug boot.

Using the above, one could easily build a spark tester whereas they could connect 2, 4, 6, or 8 cylinders all at one time. The ground nail being straight up, the others being bent, aimed at the ground nail. A typical 4 cylinder tester follows:

..........X1..........X2

.................X..(grd)

..........X3..........X4

This can obviously be modified to a 6 or 8 cylinder setup tester.
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compression on both cylinders equal at 65 lbs. is this an acceptable reading. I realize engine is older. Was expecting higher reading, but at least equal. Thanks
 
Shoot a little bit of pre-mix into the cylinders, then double check the compression. Perhaps the rings etc are bone dry. Also, compression varies by how fast the engine crank over... instead of using the geared down manual starter, use a cord wrapped around the flywheel for higher speed.

Let us know if the psi reading improves.
 
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