Yah - if you're really careful (and the design lets you access the venturi from both ends after removing the throttle shaft and disc) you can machine a taper into the existing venturi to enlarge it. Typically. the angle should be shallow, with about 2 × as much on the lead (choke side) as the trailing (throttle side), such as 5 & 10°, but there may not be enough metal to remove much unless the angle is larger.
The 2 angles should intersect at the same point as the original venturis smallest diameter, which you won't get if you just cut from both sides. Make a diagram 1st!
Depending on the casting, some can be enlarged more than 3/16".
This won't provide enough signal for the main system to come on line normally, so add a booster. This can machined from tubing, but I prefer to just swipe one from a dead Holley 4150 etc. by driving the leg out of the body with a drift.
In some carbs (haven't tried a B) you can bore the main right through and insert a whole venturi + booster "adapted" from another carb.
You have to suspend it in the bore, very close to centered, with the bottom slightly downstream of the main venturi's smallest point (about 1/32" below is good).
The fuel entry must go through the booster, which may require some plumbing.
Yes, all the jetting is now wrong.
