200 miles is beyond the learning curve and you said it ran great, so if it ran well, once you can fix or eliminate engine problems, I'd really check the O2 bung if problems persist. Have you pressure tested the bung?
I know from the last bung that I've welded that it looked fine looking at it, but pressure testing showed it wasn't airtight as I thought it was at all. Air was able to pass very easy thru tiny passages that I could not even see, so grinded all again and made a second pass with higher welds and done entire diameter in one pass vs 1/4 which was prolly where the mistake came from.
If you use the provided thingy, after 200 miles of heat the insulation has become hard and if there is a weak pressure spot, it doesn't take much of gas pressure to create a false air gap.
It's annoying to remove things again, but as said above, it's been one of the most common source of probs on Holley forum for units starting to behave weird.
@scarpent1"dual plane intakes causing issues with fuel distribution. Adding an open carb spacer may help."
I have 1 cm spacer on my Offenhauser dual plane on my 351, no probs at all, it follows the same logic as the venturies but on my 429, also having an Offenhauser dual, there is a different design for the split under the unit (right left vs 90deg split). I might need a taller spacer or remove bits of material at the split, time will tell. But no matter the model/design of the dual plane intake, a spacer certainly makes sense in combo with the Sniper.
