Model 18 Carb problem

The air screw on my new 276 on 1937 16H has no appreciable effect.  I look forward to a solution.  Wassel do sell the Type 76 (which was correct for late 30's, but I bought Amal who only market 276).  I've stopped caring since it runs OK, but I'm not entirely happy with pickup, especially when trying to increase revs quickly when I'm changing down a gear.

The pilot drillings in the jet block are really tiny , and if they are sized as original they could be too small as todays fuel tends to run weak. They also can block with the smallest amount of swarf. The Block can be driven out. 

it sounds like it's running weak for as soon as you add some air via the air pilot screw your weakening the mixture more causing the spitting back......try raising the throttle needle up one notch then screw the Air Pilot screw right home and then back it off a full turn then see how it runs.....if it's still spitting back turn the Air Pilot screw back in a quarter turn at a time and see how it runs.........that should sort it......if it's running ok but it's stalling on tick over try screwiing in the throttle slide stop screw untill a satisfactory idle speed is reached....happy fiddling

Have it cleaned in an ultrasound tank. Its blocked by years of running debris and modern fuel. Did mine, bought a great tank off e bay, use proper fluid. Fitted new jet and needle etc runs now like a clock

Unlikely to be blockage from old fuel as its new.  Swarf  will not be released by ultrasound .Take it apart and check the pilot and bypass drillings are sized as per Amals  1937 spec .For this info you need to contact  the rep  to look in the original   data .  I would not be surprised if you get some very different  measurements. These are not jets you can change,but are drillings that can be re-sized with some tiny drill bits.   As I had to do. Also check the fuel level is not too low and you have the correct float needle . I had to make a new clip slot on a needle.  Its all part of the game!.

I had the same trouble with my 1940 16h and found that the inlet guide was so badly worn I could get a 3/32" drill in with the valve so have a feel of yours as the guide was letting in more air than the air screw and also have a look at your plug colour after a quick run, this will give you a clue.