<VV> Turn Cut-Out?

[N. Joseph Potts]

Every time I leave work, I have to execute a u-turn, followed by
accelerating as fast as I can if there is traffic coming on (this is Miami).
     When I make this u-turn and then floor it, the engine acts as though
throttled, and accelerates (this is in first gear) only VERY slowly, not
recovering until I take my foot off the accelerator, such as to shift to
second, which I don't get to for quite a while in the circumstances.
     In a normal straight-line start, I don't experience anything like
this - I get what I believe is normal performance for a 140.
     Is this turn cutout (I have stock carburetors, with stock float levels
(parallel to cover-gasket plane))? Would I benefit from installing the
cut-out fix described (among other places) in Bob Helt's Classic Corvair?
     I have ball-and-cage float valves (the ONLY modification to my carbs),
and I seem to recall The Source advertising that if you have these, you
don't need carb vents. Is this so? If so, would I benefit from plugging my
carb vents?
     Thanks for all input, and I hope you'll POST your replies, although if
you don't, it won't actually make any difference to me.

Joe Potts
Miami, Florida USA
1966 Corsa coupe 140hp 4-speed with A/C