Dropped Cylinder

[GlasstronJim]

I have a 1975 70hp loop charged Johnson, and once in a while it acts like it drops a cylinder. I went to check the plug wires today while it was running and the center plug cap gave me a jolt, so I shut it down and wrapped it up with black tape. It didn't shock me again but it never ran on all three again 2mile slow ride up river back to the dock. Any ideas????

 

[HighTrim]

Re: Dropped Cylinder

1. Check the timer base resistance from the black/white wire to the white/black wires. Reading should be 10-20 ohms (or 30-40 ohms for CDI Electronics Blue Timer Bases) .
2. Check the DVA output from the timer base. A reading of at least 0.5V or more is needed from the black/white wire to the white/black wires (while connected to the pack) to fire the pack.
3. Check the DVA output on the orange wires from the power pack while connected to the ignition coils. You should have a reading of at least 150V or more. If the reading is low on one cylinder, disconnect the orange wire from the ignition coil for that cylinder and reconnect it to a load resistor. Retest. If the reading is good, the ignition coil is likely bad. A continued low reading indicates a bad power pack.

 

[GlasstronJim]

Re: Dropped Cylinder

what is a load resistor? And do I do the volt testing running or just with the key on?

 

[HighTrim]

Re: Dropped Cylinder

The best thing to do is not grab the plug boot while the motor is running without an insulated tool Try a spark test to start. The spark should jump 7/16 of an inch with a strong blue zap!! on all cylinders. Make sure the plug wires are free from nicks or abrasions. Look in the boot, if the end of the wire or the plug spring is corroded or rotted, bull the boot off, cut back the wire, allowing enough to reach the plug after, trim 1/8" of insulation off, fold over the exposed wire, push in a new plug spring, spray with wd 40 then install new boot. If you find a faulty cylinder, try swapping the coils and see if the problem follows the coil. If it does, replace the coil. Let us know what you find.