Working on classic motorcycles comes with its share of challenges. Parts availability, lack of aftermarket support, missing or unreliable information, and the rambling of graybeards on a thousand owners' forums—often loudly and proudly incorrect rambling—can make working on even popular classics like Honda's 70s-era CB series bikes an uphill battle.
Thankfully, though, there are companies out there that produce parts for even the most obscure bikes. They hear the cries of
masochists shadetree mechanics like me who wrench on bikes with parts made of pure unobtanium and produce those parts so that they're not so unobtainable anymore. Keyster is one such company, for example, and the Japanese parts maker has released a carb rebuild kit that should make the early-80s CB750F fans very happy indeed.
If you've ever worked on a carburetor, you know that the float needle and needle seat regulate the flow of fuel into the carb's body. In most carbs, the seat—a machined brass fitting with a conical internal cavity and a tiny hole for letting in fuel—is threaded on the outside and just screws into the carb body. This makes removal for cleaning or replacement very simple. Some carbs, however, have press-fit seats that are difficult or near impossible to remove.
These press-fit seats were often considered "permanent" parts, and replacements were rarely, if ever, offered by the OEM companies. The seats on the Kehin VB52BB, VB52EA, and VB52EB carbs fitted to late-70s and early-80s, Japanese domestic market DOHC CB750 F models are a perfect example of this. The press-fit seats on those carbs were fine for the time, but after 40 years of use and wear (and often serious neglect), many have worn to the point of uselessness.
Until very recently, if you had one of these carbs and it had a bad seat, your choices were pretty limited—buy some carbs off eBay with (hopefully) good seats, rig up some kind of Rube Goldberg contraption to extract the seat and sub in something that might possibly work, or junk the carb. Now, however, Keyster has a better solution—the Valve Seat Restoration Kit for Kehin VB52-series carbs fitted to JDM Honda CB750FZ, FA, FB, and FC models.
The kit comes with four new brass, press-fit seats, four new needles, a tap to cut threads in the old seats, and the parts needed to build the jig used to pull the old seat and install the new one. The new seats are made by Keyster to Honda OEM specs and are apparently a perfect replacement for old, tired units. All the parts come in a small plastic container with multiple compartments and a latching lid to keep everything organized and easy to find.
Using the kit requires a better-than-average level of mechanical aptitude—this kind of work isn't really well suited for beginner wrenches. Thankfully, our friends over at Young Machine put together a pretty detailed guide outlining the kit's use. If you look hard enough, you can probably also find some good video guides on YouTube. While the kit is specifically built for the bikes mentioned above, it obviously
Priced at ¥8,000, or about $57 Yankee dollars in TYooL 2023, Keyster's Kehin VB52BB, VB52EA, and VB52EB Valve Seat Restoration Kit is available from the company's website.
Sources: Young Machine, Keyster