I had a 75 Kawasaki H1 500. It didn't like the rain much. It had the coils mounted under the tank but far enough forward that the front tire threw water up on the coils. The water seeped into the caps where the plug wires hooked to the coil. This gave an easier path to ground than threw the plugs.
I doubt this is your problem.
The first thing I would do is check the voltage on the red/white wire at the coils. With the key switch on, engine stop switch in run, check the battery voltage at the battery, now check the voltage on the red/white wire. They should be the same or at most .3 volts lower at the red/white wire.
If the voltage is lower than that, it's probably dirty contacts in the key switch or engine stop switch. My 81 was having a no power situation the other day, I had to remove the key switch, take it apart and clean the contacts. Works great now.
The engine stop switch can be disassembled and cleaned too.
Now with good power to the coils the next thing to check is the points. When the points are open you should get a voltage reading very close to battery voltage when you check for voltage at the points. If the points are closed you won't get any voltage reading because the points ground the coils when closed.
If you crank the engine while checking the voltage at the points it will jump back and forth from a voltage reading to no reading. This means your points are opening and closing.
Your points need to spend the right amount closed to fully charge the coils so when they open the coil fires the plugs. The points are closed for a certain amount of degrees of angle. This is called dwell angle. If the dwell angle is set wrong the coils won't be turned on and off the right amount of time.
Adjusting the gap is now you set the dwell angle. If too close the coil won't get a full charge. If too wide the coil won't have enough time to discharge before the next charge cycle begins.
The points have to be clean and smooth to get the best contact. So you need to clean them. A points file works best. A few strokes of a points file smooths the surfaces. Your feeler gauges have a thin coat of oil to prevent rust, this oil can get left on the points. Once adjusted use a white paper, like business cards are made from, cut in 1/4 inch wide strips. Spray a bit of electrical contact cleaner on the paper. Open the points with a finger, insert the damp paper strip, let point close, pull out paper, repeat as need till the paper comes out clean.
If you can't get the points clean replace them.
Once the gaps are set you need ti time them. The repair manual gives you good instructions on this.
Leo
