Alright folks, here's my situation. I recently bought an '87 f250 with a non-original carbureted 460 of unknown vintage. When I got it home, I noticed the distributor was not bolted down. I picked up a timing light, unhooked the vacuum advance, and adjusted the timing according to my Haynes manual with the correct offset. With the distributor bolted down and the vacuum advance unhooked, the timing is as it should be. The problem is that when I plug the vacuum advance back up, the timing shifts significantly (maybe 45*) and stays there at idle. Is this normal? I thought at idle and at full load, the vacuum advance should not be doing much. I watched some youtube videos that showed the timing advance when the throttle is hit, but then the timing settles back to normal at idle. Am I doing something wrong? Does the throttle position need to be adjusted? The truck sounds good now, but I just want to make sure everything is in order because I'm about to haul a big load of fill dirt and don't want any surprises. Thanks!

 

Your distributor is attached to manifold vacuum which is highest at idle (except for deceleration). There is nothing inherently wrong with this, it makes the engine more efficient at idle with more advance. The only problem would be if you cannot get it to idle down with that much advance in it. If not, you should switch it to ported vacuum, which cuts off at idle.

 

Good to know. My instrument cluster isn't working, so I can't way what the RPMs are at idle, but it does sound a bit high. Sorry if this is a dumb question, but where do I hook up to ported vacuum? Would that be a port located above the throttle valves?