I dont know if this will help you at all but i have come across a couple of clutchs that wouldnt disenguage very well caused by either a worn push rod or worn arm. What we end up doing is removing the pressure plate, and the top hat that sits inside the pressure plate bearing. Add a shim to this top hat and then replace it all. This brings back the clutch arm and so you get a better pull on the handle bar lever. Hope that makes sence. So just to recap, try a washer between the top hat and the pressure plate bearing. Might only need to be .020" or .5mm to do the trick. Very common on MX bikes!
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If I have to take the carbs off once more...