Hello can anyone tell me how to fix or repair gas control on tiller 15hp 1955, when I turn handel it turns real easy and doesnt advance butterflys like it should, it looks like a small piece of plastic broke off on gearing tube above the two mesh gears at the end of tiller ,do they sell replacement part for this I looked and did not see it or was looking in wrong place, might be like a little tab or keyway, I have pics of it just dont know how to attach it here can email thanks Brian