I've seen to set the timing at 0 with the vacuum advanced plugged (actually at my elevation it'll be a little different, but still), but then I've seen people saying to set it at 12 degrees if you don't plug the lines, so...what's the benefit of plugging the lines? If you can just set it at 12 and not bother plugging the lines, why do it? I'm assuming that there is a reason, but if not, I'm not going to bother plugging them.

 

I imagine because with the lines plugged you have a known condition for setting the timing, the distributor will not be artificially advanced or retarded by the external vacuum lines. The problem with engine vacuum is that it is not a constant value from engine to engine nor at different elevations or weather conditions. You could always do a check on yours, set the timing plugged, then reconnect the lines and see how the timing has changed.

 

Thanks, I'll go ahead and plug them when I do it. I figured there was a good reason, but wanted to make sure.