(2)450 DP's vs (2)750 DP's

I can’t remember if your carbs are inline or sideways.

If they are inline you may have enough fuel in the bowls that Turing one way will lift the float and shut off the fuel. But it would have to be an aggressive long turn for that.

The other thing I’ve seen is too much fuel in the bowl and when you turn it will dump fuel out one of the boosters.

At that point I lower the float level a touch and drop the fuel pressure.

I have learned that 5 PSI is plenty of fuel pressure. I’ve run some as low as 4 without issue.
They’re 4150’s so they’re mounted sideways. There is no fuel coming out of the vents as I’ve run it without air cleaners during some of the runs and no sign of that. Fuel pressure is 5.5 so that’s probably not an issue. I’ll level the car out and see where the floats sit.