My Merc 140 won't return to idle. It looks like the previous owner put a spring on to help pull the throttle all the way back but I don't think thats factory and would like to get it the way it's supposed to work. I'm assuming something is wrong with the linkage, but everything looks ok and tight, just a minimum of "slop". It will idle back correctly when I move it by hand on the carb, but using the throttle won't get it down to idle. Any thoughts?