300ex Missing Out

[TJ400EX]

I need some help. A buddy of mine's son has a 300ex that is missing out. It seems to run fine some of the time and then it will sound like it hitting the rev limiter. When a half throttle and in the middle of the rpm range, it's fine. But give it full throttle still in the mid rpms, it starts missing. I have cleaned the carb twice and we dropped the jet size back down to stock (it has a supertrapp on it a is the only mods), and put a different CDI box on it. It actually sounds like the choke is on but it's not and it doesn't do it at half throttle. We have removed the air box lid and that didn't help. If anyone has any suggestions, I would appreciate it. We are heading for a two day trip a the Badlands in Attica Friday and Saturday and we need it for him then.

Thanks,
Tim

[300exazzkikr]

Did you check to make sure your floats weren't sticking?

[mikey726]

I used to have a 300EX, and it sounds like the same problem I had. I don't remember the exact details but something inside the engine was bent(?) and would let the reverse lever float at higher RPMs, which would cause the reverse rev limiter to kick in. Try riding it and pushing down on the reverse lever with your foot and if it runs right, there's the problem. Until I got mine fixed, I wrapped a rubber band or two around the end of the lever and under the starter gear housing to hold the lever down.

[mikeman828]

Wow, sounds like the same type of problem I'm having with my 300ex.... It just started this winter. I have been trying to solve it for a couple of months now. It doesn't happen right away, usually after riding for around 15 mins or so (when the engine gets warmed up). up to 1/2 throttle it runs fine, but when I try to give it a lot of gas it really starts to shudder and sputter!!! It's pissing me off!! I have taken the carb out and cleaned it all out, no luck. My machine is all stock so mods aren't the issue (when it started I had my stock exhaust on, since then I have put an IDS2 on, but that's it!) My next course is to check the fuel petcock and look at the spark plug. Other than that....I don't know

Let me know if you figure it out and I'll do the same

:confused: :confused:

[TJ400EX]

Well, we took it apart last night. It was still missing out and hadn't been ran all day. We thought it may have jumped time on us, but after checking, it hadn't. We noticed that the neutral and reverse lights were acting up each time this happened, so we checked both plugs and they seemed ok, but we cleaned them up and put them back on. We ended up changing the wiring harness from the battery to the handle bars, the whole thing. It seems to run fine now. I will let you know how it does over the weekend. It could have something to do with the reverse lever? That's exactly what it sounds like, your in reverse trying to give it heck. Thanks for the help! I will let you know Monday.

Tim

[mikey726]

Yeah, that's actually how I figured it out. One time it when was acting up, I noticed that the reverse light was flickering. Anyway, good luck.

[jgray]

I had the same prolems.. 3/4 to full throttle start breaking up and sputtering.. I had a friedn with a 300ex. We swapped CDI boxes, now his was sputtering and carreing on, and mine ran great. Off to get a new one we went. that was my fix. Though it seems like you did that already.. Glad you found it !!

Jason