300 EX with limited RPM

[Ronald Gosse]

Hi! I have a 300EX that is having a problem that at first appeared to be electrical where it accelerates strong up to what I'm guessing to be 4 grand and starts hunting.Seems to be an electrical issue due to puff of black smoke as soon as the engine kicks in once the rpms have decreased.It's too consistent to be fuel. Checked static timing. Set to manual. No Change. Have not been able to figure out how to test if the spark is being cutout such as would occur by a rev limiter. Have tried the following without success and wanted to know if anyone can help. First tried to seperate between fuel delivery or electrical problem. Rebuilt carburator, new jets and needle valves etc. Cleaned petcock assembly. No change. Checked all wiring connections. All seemed to test fine. No change. Replaced CDI. No change. Replaced Rev Inhibitor Box. No change. Checked the reverse switch. Tested fine Replaced Stator and Pulser coil. No Change. I'm stumped! Can anyone help me? I just can't figure this out! Starting to get desperate and feel that I've already wasted too much time and money. Looking for help! Do you think it may be time to call in a professional? Just want to get back to riding. Any help would be greatly appreciated.

[bwamos]

Clean the connector for the reverse switch under the black sheetmetal cover behind the Rear brake pedal and all connectors between that and the CDI. The big old wire harness right above the reverse module & coil is a big place where the connectors get fried. Water gets in there, causes corrosion, then the terminals get hot and cook. I got rid of that connector and soldered the wires together. It a real pain to get apart, so be patient, and expect it to be a huge pain.

I will 90% garauntee this is your problem. You're hitting the reverse limiter even when in forward because the CDI thinks you're in reverse because of a high resistance at a connection (not a fully closed circuit)

If you clean it and it still doesnt work.. try grounding that wire directly to the frame as close to the reverse module as you can. This will tell you if it is the poor connection issue.

[2muchquad]

If you didnt have a main jet come loose and the carb is cleaned completely have you had the rocker cover off?Are the lobes worn badly on the cam?i have seen lobes worn so badly that i could tell that they werent opening the valves much at all.usually when bikes are beat real bad such as dirty oil and not adjusting valves regularly they will eat the valve train pretty bad.A 300ex is almost bullet proof but they do need the basics from time to time.i would assume you have a clean air filter without too much oil on it as well?Try the reverse switch that bwamos suggested as well,ground it too the frame and you'll know promptly if thats the case or not,good luck
;)

[Ronald Gosse]

Thanks for the information. Did try to ground the connection to the REV Inhibitor. No Luck yet! Going after the connector next with another wiring harness. Will keep anyone posted with my progress. If this doesn't work I guess I will go back into the carb!
Wish me luck. I really appreciate the help and quick responses. That was impressive!

[bwamos]

If you're hitting about 4000rpm and bouncing.. instead of a full blown bog.. I garantee it is the reverse limiter kicking in.

Folow the wire from the rev/switch below the clutch basket back the the reverse module (small box near the coil). Take an Ohm meter and put one tester prong on that connection.. and put the other on the battery's ground. It should be a short circuit. If you get over like 13 ohms.. then you have a poor connection between the reverse inhibitor and the reverse detection switch.