Quote:

.....but by nature of design those cr's will dump too much gas if you just whack it hard.



Ummm, I think it's just the opposite. Air flow through those carbs is slower, so there's less "draw" on the fuel (technically, less pressure drop). That translates to a leaner condition.

Remember that most carbs, including these, have 4 different areas that can have the fuel mixture adjusted: Idle; off idle - transition; mid range; and wide open.

There are both fuel and air jets that change the mixture in all four of ranges. In carbs with vertically moving slides, whether round or rectangular, the front side cut-away also influences performance.

Add to the situation the lack of an accerator pump, and good carb tuning gets even more difficult.

NOTE: If you are having problems getting an accel. pump carb swap to work right on your bike, as in it's too rich, then the rest of the carb is probably too rich in the first place and needs to be leaned on.

The whole idea of an accel. pump is to cover up/overcome a lean spot. Engines run much better at part throttle, at lower rpms and a steady state (and pollute less), when they are lean. But they don't throttle respond well, hence the pump.

Remember, too, that there are many influences on the proper jetting for a carb. Cam timing, spark plug heat range, spark timing, (even spark intensity), compression ratio, intake system breathing, exhaust system breathing, over-all engine operating temperature, and operating parameters (how fast or slow you drive) all combine to determine correct jet selections.