spark changes locations

[roofcock]

hello all and thank you for looking. i have an old bass boat with an 85 hp Johnson(1976). the motor starts and idles fine. when i go to w.o.t. it only revs to (guessing) 3000 r.p.m.s and barely moves the boat. i check the spark and it only fires on two cylinders. do a compression test and all checks out decent. check spark again two different cylinders fire the other two are dead as in hold them in your hand and turn the key dead (nothing nada zilch). i keep checking and it likes to bounce here and there and not over there (the spark) and then change cylinders. i bought it used.the previous owner was a parts hanger and got irritated enough to buy another boat. with that said i believe the power pack and two of the four coils to be brand new/ as he informed me and gave me the old parts informing me they were still good as it made no changes to its performance. now my question is this could this be the stator, the trigger, etc... i have two other motors, another 76 and a 78- 85 hp johnson. one the guy gave me and one i took off my old boat... running well. so both are believed to run. is there something i can remove from one of these and install on this to maybe solve my problem. what is the best bet to start with as in if it is less time consuming to just swap motors. both of the others would have to be awakened with oil change, water pump etc.. as this one on the boat has been recently serviced to include all of this. any help greatly appreciated as it is suppose to be 85 here tomorrow and lake Anna sounds good

 

[Joe Reeves]

Re: spark changes locations

Remove the spark plugs. Rig a spark tester whereas you can set a 7/16" gap for the spark to jump. The 7/16" gap is important.... do not attempt to check the spark by using the spark plugs as that route is a waste of time. A tester can be made cheaply as follows.

The spark should jump that gap with a strong blue lightning like flame... a real SNAP!

Make the test with the wiring all intact. If no spark or weak spark, disconnect the large RED electrical connector at the engine, then crank the engine by using a small jumper from the battery cable terminal of the starter solenoid to the small 3/8" nut that energizes the solenoid.

If you now have the proper spark, replace the ignition switch.

(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 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

Spark plugs should be Champion QL77JC4 plugs, gapped at .040.

If still no spark, inspect the stator under the flywheel to see if there are any cracks and/or a sticky like substance leaking from it at either the extreme front or back portion. If a leaksge exists, replace the stator.

Let us know what you find.