So I recently bought a 2002 GS500H and I ran into some trouble and I don't know a lot about motorcycles so I'm wondering what it could be. I went for a test ride before and everything was fine, but after 50 km or so I noticed the bike was running at around 3000 rpm while idle. I rode another 50 km to get home. When I arrived I closed the choke a little and then opened it again because I figured it might be stuck. This didn't do anything though. I was sort of in a hurry so I just locked and covered the bike and didn't return until the next day. The next day I noticed that when I tried to start the bike the choke wouldn't say on, it would just go back to the open position as soon as I released it. I went for a short ride (less than 10 km) and it was already idling at 3000 rpm again. I then took out the spark plugs on both sides (not at the same time) to see if the problem was due to one or both cylinders. Both ran the same.
I figured that since the problem must be the same for both cylinders and carbs, and the choke lever was acting weird, it would have to be a problem in the choke cable. Is that a reasonable assumption?
Maybe I'm misinterpreting, but when you say the choke wouldn't stay on, do you mean the lever kept moving back into the "off" position? If so, there is a screw on the bottom of the left hand control that determines the "resistance" of the choke lever. Tighten that screw and the choke lever will stay in the "on" position.
As for the high idle, have you tried adjusting the idle?
no that's exactly what I meant. Haven't adjusted the idle yet because I figured that since the guy had ridden the bike earlier it wouldn't need adjusting, I'll probably adjust it once I fix the choke lever.
I'm guessing your previous owner never rode it far enough to get fully warmed up and had the idle set too high to compensate for that as well as the choke slippage. Tighten the friction on the choke, back off the idle screw a bit and fine tune it later after you've been on a good ride.