Mikuni Carb site http://www.mikuni.com/fs-carburetor.html
Model | Rebuild Kit - Mikuni Part # | Std. Main Jet Size | Std. Jet Needle size | Optional Jet Needles | Std. Accel Pump Nozzle | Std. Accel Pump Nozzle | Optional Lean Accel Pump Nozzle |
42 45 48 | KHS-016 KHS-016 KHS-031 | 160 175 190 | 97 97 97 | 95, 96, 98 all models (95 rich - 98 lean) | 70 all Carb Models | 60 for Sportster Models | 50 |
(from the Mikuni HSR 42-45-48 exploded view diagram http://www.mikuni.com/pdf/tm42xview121801.pdf)
Notes from Hammer Performance:
In our experience, we've found the CV40 to really start becoming a restriction at about 90 horsepower. 3)
And they tend to put a cap on the power.
By comparison, a Mikuni HSR42 will easily support 110hp, an HSR45 will easily support 130hp, and we've made over 150hp using an HSR48.
A properly jetted Mikuni HSR carburetor also delivers excellent fuel mileage. The HSR carbs are generally tuned pretty darn close right out of the box. 4)
But there are a lot of adjustments if you want to tweak on it.
One good thing about tuning a Mikuni is that the main jet can be accessed and changed without removing the float bowl. This saves time when dyno tuning a bike.
Many fans of the CV carburetors talk of it's altitude compensating capabilities. In our opinion, this is overrated. 5)
We've taken both Mikuni and CV40 carburetors to the top of Mt Evans in Colorado, for example, which is over 14,000 feet.
Both ran equally poorly, but both ran. We don't see any real or measurable advantage in the CV in the way of altitude compensation.
The altitude compensation method of the CV, which is to put the bowl vent into the intake stream, also causes all kinds of issues with certain air cleaners that don't provide the proper aerodynamics for it.
So it can be troublesome to tune depending on the specific combination. We never have such difficulties tuning Mikuni carburetors.
Notes on Mikuni Carburetors: 6)
Fake vs Genuine Mikuni HSR:
The top cover has a different design compared to the genuine.
Also you can locate the size of the carburetor and the “Mikuni” logo on the genuine while the fake carburetor doesn't show it at all.
The fake carb is also missing the “Assembled in Mexico” decal.