I agree with Brian. On my 1930 TT rep., and my 1936 and 1938 models Squirrel, I have had to increase the main jet size to 200 in order to make them go like they should on full blast. However, the size of the main jet will normally not influence mid-range performance, and I understand that there is where your problem is. There are many parameters influencing performance, and carburetor settings are of great importance. Mid-range performance is controlled by the needle, and my experience (if your needle and jet block are OK) is that the needle has to be clipped on to the third notch from top.
Listening to your engine, it idles OK, so your slide is not totally worn out. Brian suggests that you let Martyn Bratby overhaul your carburetor, and I’ll second that.
Martyn has overhauled 9 Amal carburetors for me, and they all function perfectly. As a matter of fact, before starting restoration on a bike, I always have carburetor and magneto (if applicable) overhauled first by someone I know I can trust. These items are almost always worn out or (in the case of magnetos) with at least a leaking secondary winding (“shellacitis”) and a bad condenser. This procedure has over the years saved me a lot of unnecessary trouble and grey hairs.
Kind regards, 😀