I have a MDS.48 engine that won't quit because I can't close the throttle completely. Just when tiny gap in the lower righthand corner closes (zero throttle), a gap in the upper lefthand corner opens. I've taken the throttle barrel out and tried to adjust it, but I still could't get the throttle to close completely. Could this be a faulty carb? Is there a way I can fix this problem instead of buying another carb?