Stroker engine "diesels" after I shut it down

You guys are getting pretty technical on me but thanks again!! OMM may be onto the cause... It seems like this started after I opened up the idle (primary side) by adjusting the butterfly stop. I have not touched the mixture adjustments since buying the pro built and dyno'd motor (416). Same MSD mechanical dist as the top picture and the carb looks about the same too. There is a little flat spot just above idle at about 1500 driving with the throttle barely cracked open so OMM may be onto something. The carb is a NASCAR style Holley 830 jetted for the engine on the dyno (unfortunately no temp or density notes). When I first installed the engine I had the timing set (total) at 36* like the dyno run had it. After the over-run pinging I dropped it back a tad which was just after I put on the mufflers / X pipe and thought the increased power (lower ET) was due to less total timing or added backpressure. One day I may have to drop the 750 I have on the 340 on to see how it does as that carb was perfect on the little motor.

As for piston quench - dunno. It has 20cc dished KB forged pistons to get the 10-1. I have to assume that the builder has the quench right as they did a lot of measuring per the build sheet I got.

OMM is that a 4sp or manual VB? I have the kickdown for my 904 and have it set to make pressure when the secondaries start to open. Working pretty well as is the 904 in general when in DRIVE and driving like a cop is behind me. Kicks down nicely when the coast is clear also.