I'd like to add a little something to this conversation if I may. There's nothing wrong with the stock
carb on our Road Stars. It fits the bill and will flow all of the air we need unless major engine mods are made -- but here's the issue.
Being a "Constant Velocity" type carb means the needle is lifted by means of a vacume operated diaphram located on top of the carb, we've all seen that. Engine vacume makes the slide rise which raises the needle which gives us more air/fuel.
The issues arise when we start making mods. A lot of guys can bolt on a jet kit and have no problems, others have to "play" with the jets/needles to get things correct.
The 42HSR is a mechanically operated slide carb. That means that we can jet very easily as the slide is being lifted by the throttle cable and not by means of relying on engine vacume, much easier to get "spot on" to begin with - Camshaft mods can really make vacume suffer at low
RPM's with the addition of aftermarket camshafts therefor making the 42 Mikuni the carb of choice in this arena.
I'm speaking from experience gained from my 1979 Honda CB750 "Retro Rocket". These bikes came with a bank of 4 Keihin CV carbs that have a steel-to-steel seal on the slide lift. Jet kits ARE made for these and they **sometimes** work. But if you think jetting ONE CV carb is a bear, try getting four of them in sync. It's a jetting nightmare -- answer? Spend $700 on a set of Keihin CR's which are like the Mikuni HSR42. It's (they...) are just all around easier to adjust with the engine mods some of us like to do.
UMM, by the way I've got a REALLY nice set of 1979 Kiehin CV42A carbs with
Dyno Jet stage III kits in them if anyones interested..........(just kidding, I wouldn't even GIVE them to you....)
TM1602
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