I'm having a similar issue with my 68. Pings at low rpm. All parts are from 68 and 69 Olds 350 engines unless otherwise indicated.

What was done:
-350 .030 over
-forged flat top pistons
-w31 spec cam from Lunati (308 dur, 474 lift)
-64 cc #5 heads with mild porting to relieve the larger valve (2" int, 1.65" exh)
-HEI from 1977 Cutlass 350 (plugs gapped to 60)
-Holley 625 cfm spreadbore
-Hooker long tube headers (1-5/8" primaries)

Next:

1. turn distributor counterclockwise 15 degrees to retard; test drive
2. install octane boost; test drive

Considering:

• install original points distributor (not sure what the weights and springs should be for w31 spec)
• install original 750 4mv I rebuilt with the w31 spec rods and jets (problem here and why I didn't start with this carb, top piece is warped a bit. I finished the rebuild but not sure of it's integrity).
• locate a new 750 cfm 4MV and install the w31 rods and jets

 

I moved your post to its own thread, its hard to work on 2 different cars in the same thread.

 

Did you use or buy a wideband O2 to make sure the carb is jetted right? I’m going to go out on a limb and say no.

 

What is your initial and total timing with vacuum advance disconnected? What is the estimated compression ratio? Distributor may need to be recurved for your engine.

 

I would bet you have over 50 degrees part throttle, maybe even close to 60. I would start with an adjustable vacuum advance canister turned down to 10 degrees. The stock 77 vacuum canister will be 25 to 30 degrees. As Mark said, if you carb wasn't adjusted with a wideband, it could be way out to lunch.

 

Thanks for all the feedback. Retarding timing helped the ping issue. I'm going to work on the vacuum and mechanical advance next. I think my vacuum advance is a non-factory advance that is adjustable.

• Regarding jets, are they changed during the curving process or are these separate?
• Are there any special tools needed to curve a distributor? How was it done back in 1968?