Got boat from Dad , Won't start unless you Jiggle the throttle handle .

I got a boat from my dad . He told me when I got it that I would have to run the throttle back and forth a few times before satrting the boat, then start the boat .
I am guessing that there is a neutral safety switch of some sort that needs replaced . Anyone else have this problem or know how to get iut fixed? The boat is an older Tracker ( I think 1988 or so ) 17Ft with a 35 Mercury on it . Any ideas on where to look to get tha part itself to order it ?