What carb rubbers to use with Mikuni RS 34?


XS650 Guru
Top Contributor
Reaction score
Tromsoe, Norway
I have a set of RS34s from Topham in Germany on my 1977 standard. Topham could not supply the rubbers, but indicated that OEM intake rubbers from the later models would work. I took that as any intake for BS36 would be fine, and ordered a set from JBM industries. These seemed a bit "loose" but I installed them anyway, as the hose clamp seemed to compress the rubber enough.
I have not run the bike with these carbs yet, but have looked into the issue a bit more.
The JBM rubbers have a 42mm ID, RS34 and VM34 carbs both have 40 mm spigots, according to info from Sudco.
If this is correct, where could I get 40 mm rubbers, with the correct angle for an XS?
As a lot of you guys must be running VM34s, there surely must be some intake rubbers on the market?
I'd have sworn that RS34 and RS36 carbs had the same spigot OD, but a quick look at the manual showed that you're right--RS34 has the same 40 mm. OD as the VM34.

Like you, I'd feel uncomfortable about using boots made for carbs (BS34) with a 2 mm. larger spigot; but I'd also feel uncomfortable about using anything else than a JBM boot without additional support for the carbs. If I were you, I'd fire up with the JBM's and test for leaks. If they don't work for you, Michael Morse at 650 Central offers premium rubber boots for VM34's.