I have to take exception to the comments on the difficulty of working with the SU carbs.
The model H, HS and HIF have to be the easiest to adjust, easiest to balance (sync)and least complicated carbs ever.
The HD created a design problem with the addition of the diaphragm and was discontinued quickly. That's why the replacement diaphragm is hard to find, they didn't want you to use it.
The Stromberg carb based on the same principal that replaced the SU in many cars by 1970, was never as good and had the problem of a roller diaphragm sealing the piston. The diaphragm was disposable and failed frequently. You had to replace the diaphragm every year to keep ahead of the problem. They also complicated the carb by adding things like a "bi-metalic temperature compensator" and other emissions crap.
