I have to admit that I have never had dealings with an Amal of this particular age so I’m guessing a bit. Assuming they follow the usual Amal way of working I think you will find that it is the size of the cutaway on the slide that controls the mixture for the first 1/4 or so of the slide opening, if you have too small a cutaway then the mixture will be over rich which would explain the coughing. The needle controls mixture at 1/4 – 3/4 opening but there is a good degree of overlap. Having the needle in the top groove also seems a bit odd as that too will make for a rich mixture. Is the slide badly worn perchance?
