Quite a bit of timing scatter... looks like the distributor weights are bouncing....

You may be hitting valve float when it starts popping. How much seat and open pressure is the valve springs set up for?

Or the ignition system is nosing over ...?

Does that A/F go wonky when it pops?

Last edited by efi-diy; 03/21/15 10:51 PM.
51 GMC 4.2 turbo
Can't solved today's problems using the same technology/thinking that created them