Choosing A Carbuerator

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To to a certain point, carburetors do not give additional horsepower or torque. In many applications, a smaller carburetor will give better torque without any noticeable loss in peak horsepower. With improperly done heads, and or other mismatched parts, this is not always true. Our favorite carburetors are the stock Keihin CV rejetted with a good aircleaner, and the Mikuni 42. In applications up to 90 horsepower there is little difference in either torque or horsepower. In applications of up to 100 ft. lbs. of torque there is still little difference, although top end horsepower may suffer with the CV. On one particular 80 inch application, a rejetted CV carburetor made 93.5 ft. lbs. and 93 h.p. Thus for most applications, the decision may really comes down to the difference in feel. The CV carburetor has a lighter, softer and more progressive feel, while the Mikuni 42 has an immediate crisp response to every throttle input.

Each carburetor is extremely well designed. The Mikuni 42 is more user friendly for tuning. The CV is altitude adjusting. A touring rider who may have varying altitudes to deal with may be best with a CV. An around town rider who likes instant throttle response may like the Mikuni 42. Each of their riding styles are different. For the bigger motors, we prefer the Mikuni 42 to everything else, including the Mikuni 45. A properly set up bike even up to 106 " will produce better throttle response, more torque, and nearly the same h.p as a Mikuni 45.

There are other good carburetors, and many of them will make just as much power. We haven't seen
any dual carburetor set up work as claimed yet, and believe that the claims regarding them are basically irresponsible. In fact we extensively tested a dual 42 Mikuni on a 96" motor that had already been extensively dyno tuned by another high performance shop. It looked mean and cool, but you couldn't get
your feet to the back brake and it had a huge flat spot (read - "fell on its face") when you twisted the
throttle at low rpms. We put a single Mikuni 42 with a Branch Manifold and lost 1 ft. lb. of torque, and
2 h.p.. However at low rpms the flat spot disappeared and it had instant throttle response. In first gear
a twist of the throttle instantly beaks, the rear tire loose and it doesn't hook up again until you are almost out of 2nd gear. We believe that no street motor up to 106 inch needs more than one Mikuni 42. Furthermore, this carburetor is so damn good out of the box,that it always works well, even before being dialed in. We see no reason to search elsewhere whenever we use an aftermarket carburetor.

Intake Manifolds
We like the stock Harley intake manifold. It works very well. Additionally, we are now developing and working on an entire line of camshafts designed specifically around that manifold, that increase torque
and provide a wider powerband, without any top end horsepower loss. We also like he Branch manifold,
and the one being produced by Bartel's Performance. We are not fans of the Mikuni manifold that goes
with their carburetor, although performing some cleanup grinding does help them tremendously



Aircleaners
This is an important area to get right. Every performance application should use a K & N type filter. On mild motors the Screaming Eagle high flow kit is fine. As soon as the motor has more than 80-85 h.p., that filter needs to be larger. This is true, not because the filter doesn't flow enough air, but because
the low height of the element requires the fast moving air, to bend too sharply. There are various alternatives to the Screaming Eagle filter that do provide sufficient airflow, without having to change the
look of the stock ai-rcleaner, as well as full systems which also change the look. The filter that comes with a Mikuni 42 is outstanding. If you already have a system, please discuss it with us. If we don't think it is sufficient for your needs, we will try and work on the best solution. We strongly believe that no motor should be run on the street without an air-cleaner. Furthermore, we have found with hotter cams, that some combinations can actually pick up horse-power with a good air-cleaner, simply because the air-cleaner calms down the pulses of air as it goes through intake/reversion pulses.