All in the family
The "VB" Keihin carburetors characterized Honda's 1979 through 1983 US model roadbike offerings, appearing on bikes ranging from 250cc through to 1100cc. Interestingly, most of the carbs' major parts interchange between all these models, a somewhat unusual feature in Honda manufacturing. All have the same size slide. The vacuum tops are all the same. The sync systems are identical. The float bowls (and bowl gaskets) interchange. The accelerator pump systems are essentially the same, as are the choke mechanisms. Even many of the metering parts come from the same parts shelf, with for example the main jets all being -393 type, the most common Honda jet shape. The pilot screws, floats and float valves are also interchangeable.

The unique parts
Obviously, some VB carb parts are specific to the motorcycle model. The throttle plates for example are uniquely sized, as are the accelerator pump diaphragm specs. The jetting varies. The slide spring is different on each model, and even the slide button and the slide cushion ring. There are two styles of air cutoff valve (plus one model without one), two different midrange circuit configurations, two float needle types, two float types, two pilot screw types, two different idle jet types, two different float bowl vent types, three different fast idle systems, three different vacuum fuel valves (plus one model without one). And most importantly, not only each model but even each year of each model wears a different jet needle, probably the most important specification of all, and that most negatively effected by carburetor rebuild kits.

Reputation
As with many things on forums, the VB series Keihins are woefully misunderstood and under-appreciated, even dissed as hard to maintain. The root of this problem stems from the fact that they require more than the typical "dunk and hope" approach to rebuilding, and that many of the engines Honda put these carbs on require way above average levels of maintenance, which unjustly reflects on the carburetors.

Gotchas
Experience teaches the rebuilder the many VB carb "gotchas". The earliest models' pressed-in idle jet must be removed despite there being no obvious way to do so. The carbs' largest fuel circuit employs the smallest air bleed. The choke system is perversely delicate and subject to binding and malfunction. The accelerate pump circuit is virtually always plugged up and difficult to unplug. The pilot screw is prone to seizing in the carb body and several kinds of mayhem ensue when attempts are made to remove it. Although other Keihin carburetors are cursed with crankcase vent circulation systems which feed grunge into the carburetors, the VB carbs' finely machined close tolerance labyrinth seal slides suffer the most from this. Ham-fisted carb removal from the engine gouges carb bodies and bends the steel steady plates. Unprofessional carb disassembly methods damage throttle linkage. Inadvisable carb reinstallation technique damages carb bodies and bends choke linkage.

Dynojet kits
But easily the worst, most unprofessional tactic in working on VB carbs is putting a Dynojet kit them. No one is sure why, but in this carb family at least, the Dynojet kit does not work. There is no excuse for using such kits when jetting changes required by intake system changes are easily and more properly and accurately effected by the use of factory Honda parts. I say "intake" to refer to air filter and airbox modifications. These changes typically demand between 7 to 10 main jet size increases, and in a few instances jet needle shimming. Exhaust changes don't require anything done to VB carbs except in very rare cases.

Part 21