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I have a 2001 Johnson 90 HP motor with the optical ignition. Got it on the water for the first time and it started missing. I got it home and did a spark test and i have an intermittent spark on the bottom two cylinders. What I mean is i put spark testers on all cylinder and while cranking the motor I have good spark on all of them however the longer I crank the motor i lose spark periodically oon the bottom two cylinders. Which has me confused as they are not the same bank of cylinders. I replaced the power pack, both coils and a new optical sensor. This did not fix the problem. Could this be a bad stater or rectifier, or a bad ground? any help s greatly appreciated. I would check the stater but have not got the right volt meter to check peak voltage or a flywheel puller. I am trying not to have to take it to the marina so I am hoping that I can get some advice before taking that step.
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After all that you replaced I would say bad stator. You don't need a flywheel puller for that motor,it bolts on. Check the stator for burnt coils or leaking potting. A sure sign of a bad stator,if stator looks good do a peak reading voltage check. You may want to go to CDI electronics website and check the trouble shooting for that motor. These igntions can be tricky to diagnose. Make sure the spark plug wires are gray factory wires and proper plugs QL78YC champion I think. They are the only ones that will work with optical ignition.
Have you tried disconnecting the temp sensors in the heads, they have had problems with them, and make sure they are not routed close to the spark plug wires.
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