Years ago, I put a ZZ4 in a 66 Vette. We had a cam that really woke that 350 up. I also put the 850 from the 502s on it. Test and tune, the little car was scary fast. Buttoned her up for delivery and it wouldn't rev beyond 5200 or so and it would dog out. Back into the shop it went. Long story short, jet changes, PV changes, every time would be scary fast. Every time we went for delivery, it would act like a pig.
Well, we were using a factory drop base air filter and we would test without it and install for delivery. The lid was just low enough to tip the choke blade in slightly and lock out the vacuum secondaries. Stacking two air horn gaskets fixed the problem.
My engine guy and me still laugh about that.