Give your throttle cable a good lubing. Clean with WD40 first, then lube. Also, there's two throttle cable adjustment nuts (1's a lock nut). It's in the full service manual, but if you look at your throttle cable, you should be able to see them.
Is there any play in you cables. (ie. can you move the throttle without the cables moving?It feels like it's loose) follow the cables just out of the throttle and there should be two adjustments on the cables. if the cables are adjusted too tight they will work against each other and not let the throttle return properly. (1 cable is pulling one way and the other is pulling against it).
Hope that kind of makes sense.
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