Everyone wants a cafe racer that is fast and looks good; however there are other aspects that are much more important.
My experience has taught me that comfort is the most important design aspect of a good cafe racer. Experience has also shown that it is also the most overlooked and ignored. After fitting low bars, rear sets and bump stop seat, the bike should be rideable for a long periods of time without discomfort. I have ridden too many bikes that forced me into the fetal position where my elbows hit my knees and gave me leg cramps. I have also experienced poorly placed bars where all my weight was resting on my wrists or I was being suspended in a painful half push-up. These traits are typical of medieval torture devices and should otherwise be avoided when building your machine. Extra attention should be spent on finding the correct combination of rear sets, handlebars and seat. Sometimes you will have to try several different combinations until you find one that works. It’s well worth the effort.
If you are unable to find a good combination, you may have a bike that cannot be café’d. Generally, the closer the seat height is to the height of top triple tree clamp, the more difficult it is find a comfortable position. Sometimes nothing can be done short of drastic measures. Ideally your body would be pitched upward rather than having your back parallel to the ground or your body pitched downwards. You should never have to strain your neck to see where you’re going.
The next most common problem with cafe racers is the cable routing. It shouldn’t take two hands to operate the clutch, and the engine is not supposed to rev up on its own when you turn the handlebars. The key to good cable routing is smooth, gentle curves with room to move when the handlebars are turned. No sharp turns anywhere and with no places for the cable to snag. Zip ties when used incorrectly can be your enemy. They should rarely be tight, but kept loose allowing the cable to move easily without flopping around. Also be conscience of what the cables are rubbing against. Poorly placed cables can rub through paint and wiring causing other problems. If you try several combinations and still cannot get the cables to operate correctly, then you need different length cables. Same goes for cable operated front brakes. Poor routing can reduce your braking ability.
If you have a hydraulic front brake, make sure the line isn’t twisted, bent at a severe angle or sitting in a generally unnatural position. If your combination forces the line coming out of the master cylinder to be forced around your gauges, you need to change the master cylinder or change the gauge mounting or eliminate the gauge altogether. Poor hydraulic line routing is unacceptable.
Lastly, I know you want to know how to make their bike faster. I would suggest that you’re skipping a step. The real question is how can I prepare my bike for going faster? The answer is simple really. Upgrade your brake shoes with modern linings. Swap out your disc with a larger drilled disc or add a second disc. Upgrade your suspension. Rebuild your front end and replace your rear shocks. Upgrade your charging system and lighting. Old lights don’t work very well. If you can’t stop, turn or see where you’re going, you don’t need to go faster. Once you take care of the basics, then we’ll talk engines.
– Chad w/ Ace Motorcycle Garage & Scooter