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Thread: 300ex spark issues

  1. #1
    Join Date
    Feb 2017
    mesa arizona

    Angry 300ex spark issues

    hey I bought this strange 4 wheel thing and it doesn't spark. Its a 93 300ex I have done all the typical check stator pulse generator etc... everything checks out. except one thing according to the manual the reverse switch on the right side of the case should be grounded when in reverse which should make it not spark/start in reverse. well mine is just the opposite its grounded while in neutral and not in reverse and yes I am checking the right wire its the gray wire on my bike the light green is the neutral. any way I was hoping if someone could tell me if this is right or wrong maybe if some one has this bike 93-99 could check to see if I am right. or maybe some one could tell me a trick I could do or maybe I am doing some thing wrong I have been over this bike a bunch and it is starting to drive me nuts this two cdi system is starting to piss me off I want my old atc ignition back super simple to work on. I would like to bring back this system but if I have to I will convert the bike to simpler system. I believe this is a dc cdi system and all I should need is 12v and a pulse and ground all those things seem to be in place but the reverse thing I think is holding me up. any help would be appreciated and again if anyone has this bike or would check the wiring diagram that would be great thx

  2. #2
    Join Date
    Jan 2009
    Toronto Canada

  3. #3
    Join Date
    Apr 2012
    I'll take a peek at the wiring, generally on the older 3 wheelers, the neutral/reverse switches ground when in the related gear, which also lights up the neutra/reverse lights, so a good debug if your machine has em is to make sure neutral/reverse lights work like normal.

    Around 87 some Honda machines did some really funky stuff for the wiring/cdi etc, like the TRX250X has a strange CDI setup that I haven't quite cracked yet, it's like a hybrid DC and AC.

    Ahh I think I see what you mean by the dual CDI box thing, there's a CDI (well ICM, aka DC powered, likely digital based CDI).

    The wire diagram is really funky, maybe lacking details. Like the Yellow/White wire coming off the stator goes to the CDI, which makes it look like it's picking up AC power from there, but the AC power goes directly to the regulator/rectifier and never touches ground till after it's converted to DC. The 250X engine is similar to that design.

    Anyway, just taking a wild guess, but it's possible the reverse inhibitor unit is the root of your problems. It's a mystery box according to the wire diagram. Also the service manual says the ICM is very sensitive to voltages and disconnecting with the ignition switch on can kill it. A poor connection then in theory would do the same thing if the connection is corroded.

    It might sound silly, but have you tested if the ignition switch is good? It should power the neutral/reverse lights when in the related gear, and make the headlight etc work off battery power when switched on. Also, the kill switch shorts between the Black and Black/White wires, make sure it does when set to run, or the ICM won't have DC power.

    I assume electric start works, so I think that's all the inhibitor switch is for.

    Sorry I'm kind of all over the place in this post, a quick recap is basically to check ignition switch (on = shorted between the two wires), kill switch (run = shorted between the two wires), if no lights, check the 15amp fuse near the battery, and if electric start doesn't work, you might have to test/diag the inhibitor switch (should only effect electric start I think though). I can probably make a bypass plug set for the inhibitor switch, I'll just have to dig into the wiring a bit more and validate what I'm thinking is right, maybe there's a troubleshooting page on it.

    Good luck, and let us know what you find/figure out. These newer machines get confusing quick on the electronics side, and I'm the "wire harness" guy lol.

    FYI, I don't have, nor do I know anyone with a 300EX, so if I made a bypass plug, I'd make it to t he best of my ability to be accurate, but mistakes can happen etc. I don't think it's possible to really screw anything up, but wanted to state it just so you know what you'd be getting into.


    Ok I looked over the wiring, and that box does quite a lot of stuff. It basically passes though the neutral/reverse grounds to the dash lights, and the starter button connection runs though it to the starter relay. I think under normal situations, the electric start will work when in neutral or when the clutch is pulled in. To bypass that box, I would have to wire it so electric start would work only when in neutral, or a different wiring set for only when the clutch is pulled in. If I'm thinking right, if I wired it so neutral or clutch in would allow electric start, the neutral light would be basically an indicator when electric start would work. Lots of options, another way I could do it is also add a short inline extension between the main harness and the handle bar controls so the safety system for neutral/clutch in is completely bypassed and would electric start even when in gear.

    I think a "race" harness for that machine would be a pretty interesting build, aka no lighting, and no safety systems.

    Here's another diagram I found in the service manual of this safety system.

    Also, here's a chart of the inhibitor unit's functions. The reverse switch logic seems backwards to me though. In my mind, when the clutch is pulled in, the electric start should always work, and when the machine is in neutral, it should also always work. If I recall correctly, that's how my 99 warrior was like, it didn't care about reverse that I can remember.

    Last edited by ps2fixer; 04-26-2019 at 02:40 AM.

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