Triumph Repair: carb problem, zenith carb, charcoal canister

Question
i have a 1980 spitfire, the problem is the carb keeps running over with gas, have replaced needle and seat,  now i have fiqured out that if i leave the bowl screws loose, it will run fine and not run over, right while it is running, ican just snug the bowl screws and it will load up and force gas out the small jet that you can see in the outer throat of the carb.  acts like a vent is clogged, but i cant locate an air bleed to the fuel bowl.  any help apprc...   thanks  dale,  it is a zenith carb.

Answer
Hi Dale,
The vent tube is on the right side of the carburetor and if it is still like it was has a hose from that tube over to the charcoal canister.
It does sound like a vent problem or you didn't get the float level set correctly when you put the new needle and seat in.
Howard