Jebbysan said in a previous thread: (thank you Jeb)

1) Set dial to 36
2) 0 becomes your timing pointer...adjust to zero for 36 degrees.
3) Set dial to 0
4) Set idle to 900...Record the number on the tab...(I.E. "4" or "6") this is your initial.
5) Post your findings

Recently did the above on my 74 Vette. Vette has a 350 engine not original. Block is a 3970010. No clue what initial timing suppose to be.

1. RPM was 620, One (1) Distributor advance spring off, Distributor vacuum advance port disconnected and hose plugged with golf T.
2. Timing light was advanced to 36 degrees, RPM was 3750, timing tab indicated 0 degree.
3. Idle RPM re-set to 850 (900 seemed too high), Initial timing was 12 degrees BTDC.
4. Distributor Vacuum line reconnected to the vacuum advance unit.
Timing light advance set to 52, engine ran-up to 2950 and timing tab reading was zero (0) degree.

Looking for comments/confirmation:

If the above was done correctly. Next step will be to do road test to see if I get pre-ignition detonation (engine knocking).

If I do: Have these options: Reducing timing by two (2) degrees until no pre-ignition detonations (engine knocking).

1. The advance unit is adjustable by sticking an allen wrench into the vacuum tube to increase or reduce advance,
2. OR Reduce initial timing, with vacuum hose disconnected and plugged.
3. OR reduce total timing by two degrees at a time with vacuum hose still connected?

Comments welcomed and appreciated.

 

Your timing is spot on........most HEI stuff I have worked on give you 12 initial when setting timing to 36 total. This total number is a "known" optimum total setting for "most" older Chevy small blocks.
The initial is harder to achieve optimal on a stock distributor though not impossible.......the 12 you are seeing is a great number. I would leave this alone.
The vacuum advance is really for pull a LOT of advance under light loads while cruising. And this is where you will find out if it needs to be adjusted. You need to give it full load in top gear......if you hear pinging....back out the can through the small vacuum nipple.

Of course a million people might pop in on their way of doing it.......
I rarely run HEI stuff as the MSD and their copies are SO much easier to set what you need. I also do not use dial back timing light as we found them to be unreliable, especially with a spark box.......a simple strobe with a timing tape is the most accurate......but the dial back is close for you in your garage.

Make sure you are running the best fuel possible and that the EGR is functioning properly....these things affect pinging.

Post back your findings and good luck to you....

Jebby

 

Thank Jebby

Using Marine fuel because no alcohol and the vette doesn't go out much!!