Webber carburetors

[Craven]

This is a throttle plate from a 31 fitment on a Lotus, the hole was drilled as a cheap fix for the over rich idle. Apparently worked OK with a new engine but once that had a few miles on it pretty much worthless.

[elans3]

Holes get drilled in throttle plates for different reasons, including balancing one carb bore against the other in the same carb, particularly on pre-151 &152 type carbs without the auxiliary air screw.
Not seen so much now, in the past it was used by many to obtain a decent idle when a throttle shaft was twisted, and the last bit of "twist" couldn't be eradicated.