I have a 41 GMC 1/2 ton. Hasn't run in many years but is a low mile truck that was put away running. I have replaced wires, plugs points etc. Turns easily but backfires like a cannon. The grease cup on the dist is right up agaist the side cover, it rocks easily, haven't touched the vacuum advance. It looks like there's a screw on a collar on the back of the dist shaft, is that to adjust timing? Any tips would be appreciated. thanks, Neil
