My buddy has an RC-100.. THe diesel fuel cap is half-on and/or broken and the machine runs like crap at low idle, it makes a hard clicking noise and idles rough... WHen you raise the throttle it smooths out and runs much better. Any thoughts?
If it has a fuel shutoff solenoid I'd check the wiring going to it, with more vibration at idle it could be a bad connection. You could hot wire the solenoid and see if it runs better.
^ That suggestion by 'mountainlake' makes sense _ I cannot imagine that it is NOT getting enough Voltage (which should increase with RPMs, thereby keeping solenoid circuit closed) but maybe there might be an issue there, if not a connection issue.. Good Luck, keep us posted on your findings!!