Re: weak spark on my 1973 johnson 85hp
here is Joes Posts
Joe Reeves Joe Reeves is offline
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Join Date: Feb 2002
Location: Central West Florida
Posts: 4,851
Default Re: Engine not running on all cylinders when cold?
As DJ states, and in addition to......
Check the spark with a spark tester, having the gap set to 7/16". The gap setting of 7/16" is important. If you don't have a tester, one can be cheaply made as follows:
(Spark Tester - Home Made)
(J. Reeves)
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 the!y 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
When time permits, visit my store (copy/paste) at: stores.ebay.com/Evinrude-Johnson-Outboard-Parts-etc?refid=store
You could test the coil simply by moving/switching it with another coils location. Check and clean the coil ground, all of the coils. If the problem follows the coil, obviously the coil is faulty.
Check the coils continuity as follows:
(Magneto Capacitance Discharge Coils - Continuity Test))
(J. Reeves)
Check the continuity of the ignition coils. Remove the primary orange wire from whatever it's connected to. It may be connected to a powerpack screw type terminal, a rubber plug connector, or it may simply plug onto a small boss terminal of the coil itself.
Connect the black lead of a ohm meter to the spark plug boot terminal, then with the red ohm meter lead, touch the ground of the coil or the powerhead itself if the coil is still installed.
Then touch (still with the red lead) the orange wire if it's attached to the coil, or if it's not attached, touch the primary stud of the coil. You should get a reading on both touches (contacts). If not, check the spring terminal inside the rubber boots of the spark plug wire. Poor or no continuity of a coil is one reason for s/plug fouling.
If the spark and all related comnponents check out okay, a lean, fouled carburetor can be checked by having the engine idling, then stick two fingers into the carburetor throat, acting as a manual choke. Having the engine smooth out when this is done with any particular carburetor.... you've found an offending carburetor.
