Reply To: 1956 Johnson RDE 18 30HP w/intermittent misfire on one cylinder

[Don]

Jesse Stevens wrote:

Don wrote:

Jesse Stevens wrote:

Last weekend we used a most unusual spring like day in North Florida to take the boat out on Rainbow River. When I started the motor I immediately noticed it sounded like it was running on one cylinder. I let it idle cold for a few minutes and then I could hear the second cylinder start to fire. I thought “well that’s strange but let’s give this cruise a shot”. The entire river is a no wake zone so idle speed the entire 5.5 miles with a max speed never exceeding 4.5 MPH. The motor seemed ok but after about 20 mins of run time the motor began to intermittently switch from running on both cylinders to one and back again. I adjusted the mixture screws until she seemed to smooth out, but alas… that was not the case. After about two hours of this back and forth misfiring we turned around and headed back to the launch site, putting along on one cylinder for about an hour. Any ideas on where to start?

Full disclosure: About a month ago I replaced the coils, plugs (J6C plugs gapped at 30), plug wires, cleaned & filed the points and set timing with a multimeter. I also took the runaway cutout switch apart to see the condition of the diaphragm and it looked great to me. The motor has also been converted to a single line fuel delivery system and new pump, using Sierra part # 18-7352. Motor runs great at WOT and shows 120psi on both cylinders.

Well, could be just about anything, including a funky spark plug.  You did the ignition over, did you get all the leads routed correctly so they won’t get chafed by the flywheel?  You might want to try disconnecting the ignition from the vacuum switch just in case something is wrong there.

Next, I would probably use a timing light to monitor each cylinder one at a time to see which cylinder is misfiring.

Yes the leads were all tucked away with no harm done. Where I went wrong with my ignition rebuild was pure speculation on my part. Meaning the points and condensers looked ok so I left them alone, only replacing the coils. I’ve replaced everything now and she seems to be running great.

I’m glad it worked out OK.  Keep in mind that extended idling like this is severe service for most any two stroke.  You really need to clean them out every hour or so with a good high speed run.  It sounds like you don’t have any choice due to no wake zones, so I would carry extra plugs…