Over the last several years I’ve seen the KJS single carb manifold (check it out on the web) on several bikes, and got to ride one, also. A Virago Single Carb. I was impressed with the starting, the idle, and the snap when the throttle was cracked open part way. I thought the performance up in the range was average on the bike I rode, but the owner liked it which counts for a lot. I assumed that a jetting change might produce a little more power in the upper rev range. Anyway, I wanted to learn more about how these manifolds performed, so I decided to make one myself. I wanted to know how evenly the cylinders pulled (since with one carb we’ve lost the ability to tune the carbs individually). I wanted to know whether one cylinder ran richer than the other. And I wanted to know what jetting (and other) changes might be required to make one Hitachi Virago carb run the bike.
I was not really looking for a power increase here. I think two well-tuned carbs will theoretically beat a single carb in respect to high-end horsepower, since each carb can be more precisely tuned to the cylinder it services, and the motor is clearly getting more air through two carbs than through one. But the single carb has a nice simplicity to it, is much easier to remove and replace for jetting changes, and hopefully would retain the strong, peppy, usable power of the ’85 1000 Virago that I was working with, and which was probably putting out horsepower and torque in the 50-60 hp/fp range. It was certainly running well, pulling strong and easily hitting red line.