I,m very unmechanicaland a fairly new bike owner. I own a 1983 650sc and recently all of the sudden when I put in gear it lunges forward and dies with the clutch lever still in.When it does not do that I have to hold the brake very tightly or it will take off.I,ve tried running through the gears and 2 and up are very hard to get ther if at all. I don,t know where to begin ,very unmechanical and financialy challenged. Please help. Thank You All.