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?

I guess your bike would be fitted with a Scott carb originally (?!?). Later on they used Binks (2 jet and 3 jet). My 1923 Scott has a 2 jet Binks carb. This works quite good throughout the rev range.

I have heard form a guy that swapped the internals of a Binks 2 jet for those of a Amal 276. That way you would get a needle carb in a needleless carbs body. I will look into that this winter, just out of curiousity.

So you see, quite some possiblities! And yes, you will not find a suitable Binks on every streetcorner…

It seems you will have to use air and throttle for an optimum result. Just like it was done in the old days I guess…

I had similar problems on my 27 Flyer, more info in this posting

Might help a bit but I guess you already searched the forum. And in my posting I did not find a real solution either. I do not remember how or when but somehow my Flyer ran fine afterwards.

@Ian Parsons wrote:

The fixing of the inlet stub is not very clever on early Scotts as it relies on a clamp from the frame. Scotts also fitted gauzes on the transfer ports to eliminate spitting back but this will affect engine power. I don’t think anyone uses them now.

You are right here. I have altererd the clamping a bit. See image. It might be worth a check!

My air leaks (and weak running) were a lot less after this mod.

Erik