A little history. 1990 TRX300FW, stored mainly outside, covered, at a hunting shack. A few years ago noticed an occasional non-start issue. Jiggle this, bump that...problem goes away. Had issue again last fall, no spark.

All connections look ok, remove kill switch, wire it direct, engine starts on first try. During the next week or so engine develops significant lower case knock. I go back a few weeks later to bring it home, no spark, drag it onto trailer.

Haul it to shop to work on it, starts right up and drives off trailer. Pull the jug off, piston cracked, bore scored. Replace piston/rings, hone bore. Put everything back together, try to start it, no spark.

Check out harness, all connections and continuities look good, connections at battery ok, connections in "little black box" in front ok. Found no issues anywhere. Try to start it...VOILA'! Starts and runs fine. Pack up everything & go home figuring it must have been a bad connection somewhere.

Come back to shop a few days later to haul it back....no spark. Have been on downhill slide since.

Replaced Ignition control module, coil, pulse generator & stator. Still not getting spark. Getting appropriate voltages and continuities at Ignition module except for those from the stator/pulse generator.

Can't seem to figure out what the issue might be. Have checked for potential short issue in rectifier/regulator, appears to be ok.

Getting inconsistent voltages all over the place when measuring at the connection right out of the stator/pulser. Will generate 0.8 VAC on blue/yellow wire out of stator but only .25 VAC on the Yellow/White. Good continuity on ground. Stator is new.

Ran a little test with Stator connector disconnected, regulator/rectifier plug disconnected. Y/W = 0.25 VAC cranking, B/Y = 0.82 VAC cranking. Using Fluke 98 Scopemeter. Connect Rectifier plug, Y/W = 0.1 VAC, B/Y = 0.7 VAC. Some higher oscillations, but not consistent enough to get a reading.

Connect Stator connector, Y/W = 0.25 VAC cranking, B/Y = 0.25 VAC cranking, some higher oscillations again.
Disconnect both Stator & Rectifier connectors again, now Y/W stays at .1 to .08 VAC instead of .246, B/Y drops to .01 to .05 VAC instead op .821 VAC.
Unable to get anything higher anywhere now.

My understanding is we need > 0.7 VAC on B/Y to ICM AND > 3 VAC on Y/W to get ICM to trigger voltage flow to coil. Not getting that but EVERYTHING IS NEW except for Rectifier/Regulator, but that does not appear to be shorting out. Good neutral signal, good reverse signal, good oil temp signal, getting 12v DC to Ignition Control Module, good ground away. Coil ok.

Seems like we can let it set for a few days and then voltage on B/Y will go back to normal, Y/W will increase to maybe 1.5 VAC, but then get flaky as we continue to try and diagnose.

Have checked potential grounding/shorting issues on regulator/rectifier, can't find anything apparent.

Got any ideas? I'm ready to tape explosives to it and make a YouTube video.

 

I had a similar problem with a 96 model. The battery was defective. Sometimes it would deliver the necessary voltage and sometimes it wouldn't.

 

Thanks for the reply. We've been watching that and keeping an eye on it.