The first step in tuning the pilot circuit is, or any, carburetor is to get the idle circuit correctly adjusted. That means adjusting the idle mixture screw for the best idle. Keihin carburetors sets the idle mixture screw during assembly and seals the screw under aluminum plug to prevent an owner from changing the setting.
If the aluminum plug is removed, which can be done by carefully drilling a small hole in the plug, threading in a small screw, and then pulling out the plug, gently turn the adjusting screw all the way in until it bottoms. Then turn it two and a half turns out from the fully closed position.
Next, start the engine and bring it up to operating temperature. With the bike in the vertical position and the idle near 1000rpm, turn the idle mixture screw in slowly until the idle either slows or becomes irregular. Now turn the screw out until the engine again slows or begins an irregular idle, counting the number of turns between the too rich and too lean positions.
There is an important axiom of performance work that many novice engine modifiers or builders seem to overlook: Once you've made an engine a performance fire-breather, some of the bike's engine mechanical components may need to be beefed up to handle the extra power, with the clutch usually being the first weak link.
Make no mistake: the OEM/standard clutch pack does an excellent job handling stock power levels, as well as quite a bit more. It has an easy lever pull, smoothly controls the engine's power, and sends all of it to the transmission.
There are several ways to make something out of metal. The part can be stamped, cast, forged or machined. In fact, most motorcycle parts are a combination of more than one of these operations.
The chosen methods of metal working for a given part are usually based on economy of scale. If you are going to make a lot of a given part it is usually less expensive to have a set of dies made and cast it or forge it than it would be if you where machining it from a solid chunk of metal.
On the other hand, if you are operating in custom or small lot sizes then the CNC machines make a fully machined part not only possible but also cost effective. There is another reason to fully machine a part: if you need or want to possibly make changes to it design later on.
So what does all of this theory of metal production have to do with motorcycles? It explains why some would make billet heads and cylinders for their custom highly modified motorcycle engines.
When riding a motorcycle, we have to rely on one type of bearing or another. There are a few different styles of bearings employed in the smooth operation of any motorcycle. For instance, there are engine bearings - roller, ball and needle - that keep the internal components spinning in harmony. Wheel bearings allow the bike to roll down the road, and bearings on the front end allow the bike to turn.
The setup and maintenance of any bearing can extend or shorten its life, but especially so when it comes to the steering stem bearings of your motorcycle's front forks.
For the sake of this publication, we will limit our focus to the tapered roller bearing most commonly used since the introduction of the hydraulic front forks in 1949.