In regard to the carb holding a loose accelerator pump tube in
place....NOPE....doesn't do it. I had a 67 Ghia 'bout 1971 or
so, and one day while doing a little "spirited" driving, A
clacking/banging noise manifested itself....so I immediately 
shut the engine down fearing a valve had just broke...had
the car towed home.

I pulled the engine out and began disassembling it. When I pulled
the head from Cyl 1, the top of the piston had gouges in it
as did the head, but the cylinder walls and valve seats were
ok...

I concluded that something small had been swallowed into the 
engine, and then was blown out of the exhaust....as I checked
the intake system I looked into the carb...lo and behold
no accelerator pump tube!! 

Put a new tube in, the head back on, etc...etc...I dodged
the "bullet"!

Ric