If I remember right, it has to do with the five valve head this engine utilizes, the one carb feeds one valve and the other carb feeds two valves. I believe the idea is to help out with both low end grunt and top end power.
I could be totally out to lunch on this, but I thought I remember reading that somewhere. Perhaps somebody else will chime in.
The left carb has a smaller intake port and feeds 1 valve and a very small transfer port. The right carb feeds 2 valves and has a much larger intake port. My guess is that the right carb does not quite have the air velocty of the left carb there for needs to be jetted slightly richer on the right than the left because the right carb will not draw quite as much air across the jet to "pull" the fuel out.
the right hand carb feeds 1.25 valves and the left feeds 1.75 valves. the reason for a larger main is because the carb is feeding more air so it also has to give more fuel. also only the left hand carb has a choke on it, the right one doesnt
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