I originally posted this in the PV forum because that is what I have this engine installed into, but replies are slow coming so I thought I'd try here.

The electronic ignition distributor that came with my engine (B-20F sourced from a 1975 240) baffles me as it seems to have a very wide centrifugal advance curve. This distributor has what seems to be a vacuum retard unit attached to it's side which is not being employed on my engine. When I set the timing for max advance (can't remember the specs - something like 38 deg @ greater than 3000rpm), the advance at idle is way late, like 10 deg after TDC and it won't run. If I set it close to the advance spec at idle, it will advance off the scale with increased RPM. I tried to balance it out between the two extremes which resulted in a barely-running idle. As I would increase the idle speed up from from like 400rpm to 800 rpm there is a substantial increase in the advance - I wasn't expecting any advance happening until 1200 rpm or so. I'm fairly certain that the distributor components are in decent working shape and assembled correctly. I believe the answer has to do with the theory of operation of the vacuum retarding distributor and whatever silliness that was employed by Volvo in the mid-70s to comply with emission standards. I'm afraid I am in the dark on this subject; any insight would be much appreciated.

Joe in St Louis