Carb slides getting stuck on AMAL
's is usually a symptom of the body being distorted through overtightening the mounting flange nuts.
The distortion is recoverable but don't try flattening the mounting flange with a file or emery cloth on a flat surface.
What you need to do is have a mock slide made from alloy a couple of thou thinner than the original slide. A hole is drilled through the mock slide central so that its Concentric
with the air intake.
Next, a bolt is inserted through the mock slide and the manifold mounted on a thick steel plate with a hole for the bolt. A nut is added on the other end of the steel plate and the bolt is tightened. This pulls the manifold straight again and it's useful to add a feeler gauge on either side of the manifold (0.011?) as the alloy manifold may pull back.
See This post
from years ago where John Healy gives better instructions,