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Issue link: https://magazine.cyclenews.com/i/126551
I.!') CN 1-0 CU ..c e CU > o Z Product evaluation Keihin's nevv smoothbore CR carbs By Dale Brown Keihin has been making carburetors for Hondas for as long as we can remember, but it is R. C. Engineering who will be handling the latest from Keihin, a line of smoothbore racing carfour-cylinder bur~tors for machines. Unlike Mikuni, which offers' only one size of smoothbore, the Keihin CRs come in 29, gl, gg and g5mm sizes. R.C. Engineering says that not only do they flow a lot more fuel at high speed than regular CV carbs, but they're also well suited for street use because of good low speed circuits. A set of glmm CRs was installed on a staffer's 1981 Honda CB900F. Mounted on a rack, and thus adjustable for a wide range of machines, they fit right on, although the gas tank had to be raised by half an inch for clearance. That meant a rubber collar had to be left off when the tank was bolted back on at the rear. Right off the bat the carbs reduced the bike's weight. Although only two pounds lighter than the stock Keihin CVs, R.C. says the CRs are a full seven 'pounds lighter than the stock carbs on a Kawasaki KZIOOO. Once the carbs were on the bike, R.C.'s Neil Mullin spent a day and a half jetting. A wide array of adjustments can be made to the carbs, with several needles, jets, nozzles, slides, etc., available. With the velocity stacks insti!,lled, there was no longer room for the airbox. It joined the stock carbs in a box, along with the cable for the handlebar-mounted choke. When we picked up the bike after Mullin had fmalized the jetting, it started right away (from cold), and after a few minutes of warm up, we took off. We discovered the engtne would not pull past 4,000 rpm until we'd put several miles under oUT belts. Living with the bik~ for awhile taught us the proper starting procedure. Start the engine on full choke, then almost immediately lower the lever by half. After, a couple of miles, tum the choke off, and in another 2-g miles the bike was responding to throttle input in a crisp manner. Once we went riding we found that we missed the CV carbs for their low end performance, 'but the CR carbs were quite acceptable. One thing that we didn't like was the amount of effort required to twist the throttle - it was almost twice as stiff as the stock set·up. Some work needs to be done here. On the top end was where you could real1y tell the difference the' smoothbores made. The bike had it's normal six to nine grand power surge, but with the 'new carbs, it was a much healthier kick. The Honda was strong to begin with, but the CRs really do add punch. They also add intake noise to your ear with the airbox gone. We haven't had a chance to lash up any kind of air filtration system yet, and with the chance of getting airborne debris into expensive engine innards, it's something we definitely want to do. It may prove difficult, however, because there are only a couple of inches between the outside velocity stacks and the frame tubes. All in all, we were impressed with the Keihin CRs. They do add the ponies, but you can get along with them on the road. The wide range of adjustability may cause a few problems initially until jetting info becomes more widely available. Racers will.likely flock after them, but road racing associations in our area specify stock carburetors for Production classes, so any machine with these carbs would have to run Super Street or GP classeS. The price - $575 - is not cheap. Most riders could probably find a lot of uses for that kind of money. But those who can afford it, and who want to leave n'O stone untumed in pursuit of a fast machine, will dig 'em. Contact R.C. Engineering, IggOO Estrella, Gardena, CA 90248, 21g;g27-6858. The gl, gg and g5mm sizes are in stock now. The 29mm carbs should be in within two weeks. 15