I seriously am baffled with my son's 96 300ex. It cuts out (or misses) at high rpm (well under the rev limiter), he can't wind out the gears. If he short shifts it he can ride ok. I can put a new plug in it, ride for a few min's & the plug is fouled out. I have completely went thru the entire fuel system, major carb overhaul, cleaned tank & strainer, new air filter. Still when I remove the air intake tube, there is fuel settled in the bottom of the tube. If I run it without the intake tube & rev it up, it spits raw fuel out. I have installed a known good CDI, no difference. I have removed the rocker cover to check for jumped time, timing marks are where they are suppose to be. I also checked for broke valve springs, they appear to be fine. I removed the stator cover to check the flywheel key, it is in place. I have replaced the spark plug boot, checked all my grounds, & wiring connections. I am at a point, that maybe I need to start over with the troubleshooting, when I had the carb apart, I did check the float, to make sure it does float, & it does. This is so confusing, I mean, it starts & idles perfect, it even accelerates just fine until about 1/2 throttle, then it starts missing, even just reving it up without a load. I even disconnected the reverse limiter & grounded it, no difference. Anybody ever encouter such a baffling problem? I would greatly appreciate any help or advice. Thanks

 

I already have a problem similar to yours. Please check this. Check the switch on the left (I think) Engine case behind the little cover. Check if they are loose. Do you hit that weird limiter on neutral? Anyway, check those switch first. PM me if there is something you don't understand.

I wasted a lot of cash with this problem just to find out It was only a wire problems [img]i/expressions/face-icon-small-mad.gif[/img] [img]i/expressions/face-icon-small-confused.gif[/img]

Let me know when your problem will be solved!

 

You grounded the reverse limiter? Unground it or it will do what you are describing. There are 2 plugs by the right lower case by the brake pedal one is for the neutral switch and the other engages the reverse limiter module. The plugs are under a small black metal shield. Unplug both of them and try it.

 

Hmm... the raw fuel spitting out leads me to think it is fuel related. Did it start doing it all of a sudden? And do you know the complete history of the machine? It sounds like a main jet\needle jet problem. Make sure the needle jet is there, it's removable on many keihin carbs and can easily get lost when you have the carb apart. You should be able to see the head of it sticking out in the venturi (the needle goes right through it). Also make sure all the holes in the emulsion tube (the main jet screws into it) are open, the the air bleed port in the intake side of the carb to the emulsion tube is open. Also I have seen ignorant people on occasion (a nasty dirty trick) drill out the main jet to a ridiculous size in a misguided attempt to clean it. Not that you would do that, but if the machine's new to you a previous owner could have.

 

make sure the mainjet just didn't fall out. i have seen this happen before.

 

I just read all the replys to my problem, I am greatful for all the help. As for the carb, I have went thru it several times, I have changed main jets up & down, I am now back to the stock jet (122), no difference. I tried to check the position of the needle, & could not get one of the top screws on the slide out, so I am not sure if it has been changed or not. I have blown air thru every orfice I could find in the carb, nothing seems to be blocked. I am considering just swapping the carb out with a known good one. I still am leaning toward the carb being the problem, even though I can't see anything wrong with it. I have tried grounding & not grounding the reverse limiter, no difference. I just installed a known good stator & pick up tonight, (a local cycle shop thinks it is ignition, they supplied the parts at no charge). I should get it finished tomorrow night, personally I don't think that is the problem, but I am trying to eliminate every possiblity. As for a loose wire, that has been mentioned & I have checked every connection that I can find that is related to the ignition, they all seem fine. I by passed the key switch with no change. So you can see, I, along with several local atv mechanics are "BAFFLED". Thanks again for the advice, I will let everybody know when, & if I figure this out.

 

A friend of mine had a 250x with a problem like yours and it turned out to be the timing of the carburator butterfly to the needle piston . He bent the linkage when he installed a new throttle cable. His choke valve detent was also worn out and the choke was flopping open and closed while riding it but I think they fixed that with the yellow plastic 300ex choke handle.

 

How did he retime the needle to the butterfly, that sounds like something to try. Thanks

 

I sold off my honda sevrice manual so i cant send you the instructions but if you take the side cover off the carb there is a link/lever that makes the piston move in time with the butterfly . His was bent from mishandling the throttle cable install so I doubt they would ever come out of adjustment unless someone was digging in there. This was about 10 years ago so my memory is very fuzzy. Does the quad act like it is hitting the reverse rev limiter at the same rpm or is it much higher . I had some electrical issues with mine as well. It had an intermittant stall caused by a corroded terminal in the white barrel connector above the ingnition coil. I parted out my 300ex and have most all the electrical parts if you want to give them a try. Some other things to check are the intank fuel strainer and the gas cap for stoppage. I noticed the fuel spitting out of the carb when I had the intake boot off also and it seemed normal for a single cyllinder.

 

I did question the reverse limiter, but when I disconnect it, the light comes on, & the rpms are cut out much lower. So I, for the most part ruled that out, but the gas cap, I have not checked it for the vent being clogged, but I have cleaned the tank strainer, it was pretty bad, but no difference after cleaning it. As far as electrical components, it may come back to that. I will have it back together within the next day or so, & I will know if installing a known good stator & pickup works. I will let you know, thanks