Specifications

threaded end. The VM22/210 jet was used from 1976-1979 XS650C-XS650F). In this
series, the metering orifice is located toward the threaded end of the jet. Either series
will thread into the carb body, and installation of incorrect jets is common. Many OEM
jets were produced with no bleed holes in the shank, while all aftermarket pilot jets have
them; this difference is not significant. See Appendix items 1., 4., and 7. for pilot jet
types and stock sizes.
Soak the jets in Chem-Dip or similar immersion-type solvent, and blow them clean with
compressed air. Blow aerosol carb cleaner through the air jets and follow with
compressed air, and do the same in the pilot jet seat areas.
On BS38 carburetors, the mixture screw is a small brass fitting with slotted head,located
on the outward side of each carburetor, forward of the slide tower (see Appendix, item
9). Remove the screws and the springs below them and clean with solvent, and blow
out the seat areas. Carbs fitted to 1970-1975 (XS1-XS650B) require the 256 series
screw; it is shorter than others, and threaded all the way to the slot. The 584 series was
used on carbs fitted in 1976 and 1977 (XS650C and D); it is longer, with a relieved area
between the slot and the threads. The screw used in carbs fitted in 1978 and 1979 is
the longest. It is stepped, has a recessed area past the slot, and is sealed by an O-ring.
The screws cannnot be interchanged. Some fuel screws were fitted with plastic caps to
restrict range of adjustment. Remove the caps and discard them.
The fuel screw in the BS34 carburetor is recessed in a vertical tubular casting on the
carb body toward the center line of each carb, forward of the slide tower (see Appendix
item 10). Unless it has been removed, the screw is covered with a thin brass cap, which
must be removed for cleaning and adjustment. Pierce the cap with a drill, being careful
not to damage the casting or the screw; just penetrate the cap. Sometimes a sheet
metal screw will hold firmly enough to grip the cap while pliers are used to extract it
(don't run the screw in deeply; avoid damage to the mixture screw beneath). Sometimes
it can be pried out after drilling. Remove the mixture screw, with the spring. A rubber O-
ring is at the bottom of the mixture screw seat, with a metal washer on top of it. Remove
these with a probe. When new, the washer is somewhat flattened; this does not indicate
defect. Be sure that it's flexible and has no nicks or cracks.
If fuel screws show signs of damage, wear or corrosion pits, replace them.
In the forward end of the carburetor bore, you'll find a number of holes (see Appendix,
item 11). In front of the throttle plate (butterfly), you'll find either one or two large holes
and one small hole. One of the large holes draws mixture from the enricher, and the
other will either be blind or open into the synchronizer attachment port if the carb is so
equipped. Do not apply solvent without removing the choke plunger (see enricher
section). The small hole draws mixture from the fuel screw. Blow aerosol carb cleaner
into the hole until it flows freely from the fuel screw area. Then block the hole with a rag,
insert the tube from a can of carb cleaner in the fuel screw seat area, sealing with a rag,
and blow cleaner in until it flows freely from the hole in the carb body that sits above the
pilot jet (BS38) or the pilot jet casting (BS34). Follow with compressed air.