Randman is on it. Check the color of the spark, blue white is what you want, orangey is weak. Clean all your connections, you can make the coil tab tighter with some needle nose then reinstall. Also, change the plug or check the plug boot. They unscrew off the coil wire, cut back a half inch of coil wire then reinstall. Also check inside the plug boot too. If there is a lot of black carbon buildup, needs clean, tightened or replaced. You can tighten the if its the loop type. Some you have to remove the threaded sparkplug cap on the plug itself so all you can do is clean that.
I have more coils, plugs, cantact cleaners in my garage, have at em! Let us know what works so others can learn too!
Gary