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Some Road Star owners love the stock, 40mm Mikuni, CV carburetor. Others favor their aftermarket Mikuni HSR 42mm or 45mm, while still others are sold out to the S&S Super-G, using an aftermarket manifold.
However, it is hard to argue with the incredible performance of the Genesis Big Air, 48mm carb from P.S.I. It is an enormous improvement, as others have also written. See Appendix-A for more information and my experiences with this amazing carburetor.
This is not an inexpensive project, compared to some others you could do. However, in terms of cost per power improvement, it begins to look very reasonable. Prepare for sticker shock in the neighborhood of $1,500 for the privilege of escalating yourself into the realm of fuel injection equivalent power.
Now, with my Genesis carb, I can more than keep up with the fuel injected models, without unduly sacrificing gas mileage. Frankly, when you compare the performance and price of fuel injection to the Genesis carb, it doesn't look so pricey anymore.
Hereís what I did to install my Genesis Series IV carb on my Road Star.
Note: This article applies to model years 1999-2007. If your Road Star is a model year 2008 or later, your bike is fuel injected, and has no carburetor.
Important Note: This article assumes you have some mechanical familiarity with the carburetor of your bike. If you question your skill in working with the intake systems of motorcycles you should not attempt this project (in my opinion).