[StarGate]

I'd venture to guess your throttle isn't sticking. It's normal for the idle to go up with the choke on. With the choke on it's getting more fuel and the more the engine warms up the higher the idle becomes until the engine is so warm that the extra gas starts to flood it out. You should gradually take the choke off as the engine warms up to maintain your idle around 2k. For my bike it usually takes 2 adjustments before finally turning the choke all the way off, when going from cold to warm.

But just in case your throttle cable is sticking, the springs are located on the throttle linkage between each pair of carbs. And the easiest way to lube the cable is with one of these.

Cable Luber Tool - - - - - - - - from Z1 Enterprises, Inc.

 

[StarGate]

You may be suffering from an air leak/crack in the carb holders. If it's a relatively new crack it will be small. When the rubber is cold it contracts allowing the crack to suck in extra air, as it warms up the rubber expands and can swell enough to close the crack off mostly. Next time you start the bike, take some carb cleaner and spray all around (top, bottom, both sides) the carb holders (the rubber that attaches the carb to the engine). If you hear the engine rpm surge when doing this, you found the crack. Don't make the mistake of thinking it's not cracked just because you can't see the crack with your eyes.