help with carb please

[Steven3472]

it looks like my 300ex is running rich and i cant find whats causing it. The bike acts like its at its rev limiter with barley any throttle, the plug is black on the bottom. is there an external adjustment that would help. also i noticed that in the bowl on the main jet the part it goes into has a jam nut is that main tube like other carbs and you bottom it out then tighten the nut or is there a specific amount of turns that it needs to be out thanks for all help, as i ordered a rebuild kit for it and hope that it will cure the problem.

[Here 2 help]

No - there is no external adjustment.

The main jet holder should be screwed in against the needle jet to hold it in place and then the jam nut snugged to keep the main jet holder from unscrewing due to vibration.

It sounds like the carb is just super rich as though the main jet fell out or was drilled out to a size that cannot control fuel flow. A high float level might contribute also. What size is the main jet? 122 is standard, a 124 0r 126 might be ok with an aftermarket exhaust. Pretty much anything bigger than a 130 is too big.

[Steven3472]

ok well i just ordered a complete rebuild kit with the jets and float and hopefully that will work. I took off the exhaust today and noticed a small hole near the beginning of the pipe that would cause this problem would it??? thanks for all the help folks

[Here 2 help]

No - a hole in the exhaust should not be the cause of the problem.

[Steven3472]

ok just had the carb rebuilt and still doing the same thing will idle fine but hit the throttle and then it acts like its on the rev limiter, put in new plug and still black, would the throttle valve synchronization make a difference if it wasnt correct??

[Here 2 help]

Got me on that one - I never heard of synchronization of a single carb and the service manual does not describe any proceedure for such. A weak spark could mimic a rich condition in the carb. Try gapping the plug at about .015 and see if that helps. If it does, try replacing the resistor spark plug cap.

[Steven3472]

ok ive figured the carb is good and i only have 85psi compression so im surprissed it even runs, so i took the head off and the valves are stuck with carbon will clean and retry lol