Johnson 9.9 weak spark

[gdc0581]

I have a 1989 Johnson 9.9 electric start. I was out on the water a couple of weeks ago and it was running fine and it just died. It hasn't run since. It looks to me like the spark is weak. If I pull the plugs and ground them, I do get some spark that appears to be blue. If I put a 1/4 inch bolt into the spark plug wire and crank the engine, I can jump a spark with no more than a 1/8 inch gap. Both cylinders are the same. Squirting starting fluid into the carb or the cylinders produces no fire.
Here's what I've done so far:
New plugs gapped at .030
Tested compression - 120 PSI on both cylinders.
Cleaned all visible wire connections.
Pulled the flywheel. Everything under there looks clean (and expensive). I'm pretty mechanically and technically savy. Are there any tests I can perform with a DMM or oscilloscope that will help me find the bad parts?

 

[Rick.]

Re: Johnson 9.9 weak spark

I would suggest you purchase and adjustable spark tester. One end goes on a plug wire and the other clips to a ground connection. Adjust the gap to 1/2 inch and see if the spark will jump the gap as well as what the spark looks like. It should be blue/white, snappy and jump the gap consistently. The spark checker is available at most auto parts centers and is less than ten dollars. The other thing to check is the packing around the needle valve. It must be snug and the packing nut must be tight enough to stop air from infiltrating the needle passage. Best of luck. Rick.

 

[gdc0581]

Re: Johnson 9.9 weak spark

I would consider the spark checker if I did this often. If I bought the checker (about $18 from NAPA) I suspect it would confirm what I already know. The spark is too weak to fire the mixture.

I found a link on this site that says my charge coil should have a resistance of 575 ohms and an output of 150 volts peak. I measured mine and the resistance is 575 Ohms, but the output was only 30 volts peak, measured with an oscilloscope. I purchased a new charge coil and installed it. Looking at the spark, it seemed even weaker than with my original coil. I measured the output with the new coil and got 60 volts.

I'm not sure what to do next. I could buy a new power pack, but I kinda hate to do this when my tests show both charge coils as out of spec. The only thing would be if I'm incorrectly testing the charge coils. I'm measuring between the brown wires with the power pack disconnected. What are the chances of having got a bad charge coil from my local Johnrude dealer?