1976 Johson 15 HP spark test need help

[Seahorse16]

I'm been trying to diagnose my problem with my motor appearing to only be firing on one cylinder and figure out what I need to do. When I test for spark on the Upper cylinder, it jumps the 7/16 and 3/8 inch gap no problem. When I try the same thing on the bottom cylinder, it does not. To try and tell if the ignition coil is the issue or if perhaps the coil assembly under the flywheel is the issue, I swapped out the wire connections. The following videos show these tests.

To summarize the videos, I have good spark on upper cylinder but not on bottom. When I swap wires under flywheel, I seem to have good firing on the bottom coil and poor on the upper coil. To me, this suggests that both ignition coils are good, and perhaps the coil assembly under the flywheel for the bottom cylinder may be bad, but I am just a novice at this, so any guidance would be much appreciated!

Thanks...videos to follow (Note: disassembled and re-hooked things several times and got consistent results; some of the repeat trials are posted)

 

[Seahorse16]

Re: 1976 Johson 15 HP spark test need help

Here is the upper ignition coil test

 

[Seahorse16]

Re: 1976 Johson 15 HP spark test need help

Here is the lower ignition coil test

 

[Seahorse16]

Re: 1976 Johson 15 HP spark test need help

Here is a description of swapping wires

 

[Seahorse16]

Re: 1976 Johson 15 HP spark test need help

Here is the upper ignition coil test after I swapped wires.

 

[Seahorse16]

Re: 1976 Johson 15 HP spark test need help

Here is test 2 of upper ignition coil swapped wires.

 

[Seahorse16]

Re: 1976 Johson 15 HP spark test need help

Here is test 1 of lower ignition coils swapped wires.

 

[Seahorse16]

Re: 1976 Johson 15 HP spark test need help

Here is test 2 of lower ignition coil test with swapped wires.

 

[racerone]

Re: 1976 Johson 15 HP spark test need help

The driver coil under the flywheel fires both cylinders !--You get brilliant spark on one so that driver coil proves to be working good.

 

[OptsyEagle]

Re: 1976 Johson 15 HP spark test need help

I have good spark on upper cylinder but not on bottom. When I swap wires under flywheel, I seem to have good firing on the bottom coil and poor on the upper coil. To me, this suggests that both ignition coils are good, and perhaps the coil assembly under the flywheel for the bottom cylinder may be bad, but I am just a novice at this, so any guidance would be much appreciated!

If you just changed the clips from under the flywheel and it moved the problem to the other coil then it is most likely a problem under the flywheel. Probably a dirty point.

 

[AlTn]

Re: 1976 Johson 15 HP spark test need help

under the flywheel you have a separate set of points and condensers for each cylinder...common driver coil. Externally..a separate wire running from each set of points to the individual ignition coils...soooo if you can get the same spark quality by swapping the wires coming from underneath the flywheel, you know that one set of components < points, condenser, leads > is good and one or more components firing the other cylinder require some attention. You'll probably need to pull the flywheel to check these components and there's plenty of info on doing that in this forum. You have an ignition system that was the transition from the universal magneto to the powerpack ignition system in these models. One member a few years back removed the armature plate and components, cleaned it thoroughly, ran a tap through each mounting point to clean them, reassembled the armature plate, set the points, cleaned each connector for the external wires and this fixed his problem which was very similar to what you describe.

 

[Seahorse16]

Re: 1976 Johson 15 HP spark test need help

Thanks! I will look for that other information. So you think removing the flywheel is reasonable for a rookie mechanic?

 

[OptsyEagle]

Re: 1976 Johson 15 HP spark test need help

No problem at all but you will need a balanced harmonic flywheel puller and a strap wrench that can hold the flywheel steady while you loosen and torque back down the flywheel. You will also need a torque wrench to torque the flywheel back down. I am pretty sure it is torqued to 40 to 45 ft/lbs.

Here is a picture of the puller I used on the very same motor. The second picture shows you what is under there. I would disconnect the wires going to the point and connect a multi-meter to the point lead and the other multi-meter lead to somewhere on the powerhead for ground. Now rotate the flywheel by turning the propeller (with motor in forward gear) and when the points close are you getting good continuity or high resistance or no connection at all? That is what I guess will be your problem but one needs to check. If the point is not giving good continuity then you can either change them with new ones or use a points file and file it down a little. Whatever you do you will want to set them by placing the rub bar of the point at the area on the cam that says "set" and ensure they are open to 0.020" at that set mark. If new points, err on the side of a little larger gap. This gap will narrow with use as the rub bar wears although it is usually good for a few years. Once the points are set, take a clean white business card and dip it in lacquer thinner and pull it through the points and then blow it with compressed air. That should remove any oils that might get on them. If you do anything else with them, like check the gap, etc., clean them again with lacquer thinner.

One or two drops of 10W30 or some other motor oil on the cam wick to lubricate the cam to reduce the wear on the points rub bar. Do not over oil or it may get splashed on the points and you are right back to where you are now. Pulling the flywheel.

 

[OptsyEagle]

Re: 1976 Johson 15 HP spark test need help

By the way, don't forget to change back those clips to the proper coils. Switching them is fine for a spark test but if they stay that way, that wonderful spark the good one was putting out will be happening when the piston is at "bottom dead center" and not "top dead center" where the piston on an internal combustion engine is supposed to be when the spark fires.

 

[bonzoscott]

Re: 1976 Johson 15 HP spark test need help

This may be also helpful around reinstalling the flywheel. I have a '78 15hp and my flywheel looks like the one in OptsyEagle's Photo. I found that the tool used to remove / install my electric grinder fits perfectly in those two holes you see on the flywheel. Use to hold the flywheel when torquing to 45 lbs. I never could find a strap wrench large enough to hold the flywheel. I bet those holes are for a dealer tool. I suppose you could use it to remove the nut too. I used impact.

 

[kbait]

Re: 1976 Johson 15 HP spark test need help

Also check the armature plate for any lateral play. If there is any, that distance translates directly to the point gap as armature plate moves laterally.. this makes it impossible to set timing (or point gap) correctly, as it will be ever-changing. If there's any lateral play.. post back and we'll help shore it up.

Good luck!

 

[Seahorse16]

Re: 1976 Johson 15 HP spark test need help

Thanks guys. Got a flywheel puller on order so I'll check back in with many new questions soon I'm sure.

Thx

 

[Seahorse16]

Sorry for dropping off the face of the earth, but that's what 2 kids do to a guy.

Last night I set the timing and got each point to line up between bars on flywheel. I used the finest sandpaper I had and pulled through points in case that was the issue. I then pulled acetone dipped paper through to see if that will clear up my Lower cylinder not firing. It did not work. Maybe I'm not cleaning the points properly? Not sure how a point really goes bad, could someone explain? I have new points and condensers. SHould I just try that next?

This is what I don't understand. If my upper cylinder fires fine, and I hook the upper ignition coil to the wires that feed the lower cylinder, and the lower cylinder then fires, then doesn't this simply mean my lower iginition coil is bad? I mean, once switched, the wires, points, condenser etc are all working fine right? Doesn't this make sense?

 

[Seahorse16]

Another weird thing when I was setting timing. Upper cylinder has striped wires, while the lower has solid. The striped and solid wires also attach to points so I know which one is upper and lower. However, this did not work. When I hooked up what thought the upper cylinder, it was actually the bottom. The underside of the flywheel is stamped with U for upper and L for lower cylinder, but when I thought I was setting the upper timing, the lower L point was the point that opened up with the marks on the armature plate. Same thing for the other points/cylinder. Weird.

 

[racerone]

Even the factory timing fixture marks for this ignition system had to be reversed.-----This system works different from the conventional magneto !