I'm running a 1972 Rally 200 with Pinasco kit, long stroke crank and Spaco 26mm carb.
I'd been having trouble setting a good idle speed. Yesterday I noticed that sitting on the bike caused the revs to rise, and when I got off it the revs decreased to a normal idle. This was fairly annoying, as every time I stopped at a red light I had to stand up straddling the scoot to keep the revs from going high.
Anyhoo, I rode it to my local dealer/service point, and the guys there immediately suggested that the movement of the motor relative to the frame was causing the throttle cable to be somehow pulled or moved. We took off the top of the carb box and had a look - the throttle cable didn't seem to be pulling on the slide actuator, but I disconnected it just to be sure. Got on bike: revs rose. Got off: revs dropped.
Later I replaced the section of the carb from the banjo to the float with that from another carb (genuine Dell'Orto this time) - still no change.
I'm baffled. Any ideas?