So my truck went suddenly sluggish. I checked the timing and when I gunned the engine I did not get as much of an advance as I remember seeing so I checked the vacuum advance and when I plugged the line to the carb the engine smoothed...Oh oh. So I put my vacuum pump on the vacuum advance and I can't pull any vacuum. The diaphragm unit needs replacing. Is it possible to change that while the distributor is still in the truck or do I have to pull the distributor? Have any of you done that? Thanks for any inputs.