My throttle lever doesn't seem to stay put when cruising down the lake. If I don't rest my wrist on it, it will slowly move back towards idle. It won't come all the way back but will slow down to about 1500rpm. I have noticed a screw hole at the bottom of the lever with nothing in it. Is there a set screw that is supposed to go in there holding friction on the lever or do I need to replace the whole control assembly? If there is a screw missing, where do I get another one. I haven't seen one in the exploded views of the parts section of this site. Thanks.