O.K. guys here it is. I am trying to get my spark curve correct because I am experiencing an extreme case of detonation on the top end. The problem is that no matter where I set my mechanical advance, I always have about 40-42 degrees of advance without the vaccuum canister hooked up. How is this even possible? Is there a way to cut down total time? I have used every possible spring combo with no results, is something broken? What could it possibly be? This problem is making me pull my hair out and I am about ready to buy another distributor. Even when I run no vaccuum advance I have detonation. I have played with a few HEI distributors in my time, but have never experienced this. Any help would be greatly appreciated. Thank you for your time.

 

Got another distributor and that fixed it.

 

There are two things you could do:

1) Set the total mechanical advance to 36-38 degrees with the vacuum disconnected, ignore what you have at idle. If you use manifold vacuum, you'll make up for the low mechanical advance at idle.

2) Get a bushing to put in the advance mechanism that limits the total mechanical advance. If you look at the mechanism with the weights removed, you'll see what I'm talking about. Those bushings are available, sounds like yours has been removed.

Typically, you shoot for 8-10 degrees mechanical advance at idle and 36 degrees total advance (both at the crank).

 

Sounds like your distributor was worn out. I went walking through the junk yard looking for HEI weights one day. It's amazing how many had worn out weights or shaft bushings. The drivers must have always complained about poor performance from their cars before they were junked.

I also had to troubleshoot a newer Vortec BBC. It ran very rough and already had the cap and rotor replaced by someone else. I found the distributor shaft bushing was completely worn out at the top (plastic distributor). Dropped in a new distributor and it ran like new.

 

I appreciated your responses, now I understand what happened.