50HP Johnson J50PLSI Spark on 2 not on 1....how to trouble shoot.....just started!

I have a 2000/2001 Johnson 50HP. It had been running fine. Then it started missing, vibrating and being hard to start. We have a very very weedy lake and do have to "clear" the lower transom alot. Very recently I noticed the I was only getting 1/2 power. Put new plugs in and will get 60-70K rpm in "idle" but under load about 40K rpm is all it will go. So I figured must be a bad cylinder. Did a compression check and have 120 in both, very nice and even. I have one dark plug, the other is clean as a whistle. Switched plugs and wires. It is the spark that isn't getting to the top plug. Any ideas on what to check up-line?
Thanks and new to the forum. Hopefully not insulting anyone.

How do I identify the sensor coil? Is there one per plug/cylinder or just one overall?

I'd start with the illustrated parts list, it shows a picture of the items and if you scroll down the parts list, it will tell you how many are needed. If I have your motor selected correctly, there is one stator, one sensor coil, one power pack and one coil assembly. All 4 of these work together to provide the spark to the spark plug. The best thing to do is to get a shop manual for your motor and use it to test the components so you can rule out the bad part.

Check this thread:
http://www.marineengine.com/boat-fo...surement-from-sensor-coil-into-the-power-pack

However reving your engine to 6-7K on idle is a sure way to get it severely damaged!! Hardly any fuel needed = no oil for lubrication!!!!!!!!!!!!

2 sensor coils I believe.----------Switch the small wires at the coil and see what happens to spark.-----If you check you may be able to switch / jumper the wires and try to make sensor coil #1 fire coil # 2.-------Once that is done you can decide.-------------Or if you have an ohmeter you check ohms on the 2 sensors and compare them.---------My bet is a faulty powerpack.

Have made sure oil supply and compression are fine. Have ordered a new power pack. I will post a resolution if that is it. I cleaned all leads, ground connections and all of the terminal bar strip connections, nothing changed. I really appreciate all the input.

Replaced the power pack same problem missing spark on top cylinder. Good spark on lower cylinder. Tested at night no shorts seen.....what might be next...ignition coil????

Turns out that the trigger was bad and fried both power packs. So new trigger, new power pack and firing on both cylinders. Proper diagnosis with the right tools would have saved me a BUNCH of $$$. I was rushing a little and paid for it.....literally!