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Carbs
- Thread starter Tim L
- Start date
TJZ662
XS650 Addict
I’ve read 78-79 are the best 38’s. I’ll trade ya mine 
78-79 BS38's , now realize I haven't owned BS34's.
(And never will)
BS34s work just fine. Seat of the pants, there's no difference. I prefer the plastic floats in the later 34s. Parts are easier to come by on the 34s, not that 38s are impossible.
BS34; rubber tipped float needles an improvement. The needles need a bit of shimming cuz EPA locked them lean..
Otherwise yeah the 78-9 BS38 had several improvements over the old units, internal vent routing, and a spring to keep the needle from fluttering (and wearing) the biggest aides.
All CV carbs prefer the internal volume of an airbox compared to pods.
Otherwise yeah the 78-9 BS38 had several improvements over the old units, internal vent routing, and a spring to keep the needle from fluttering (and wearing) the biggest aides.
All CV carbs prefer the internal volume of an airbox compared to pods.
Yes, the '78-'79 BS38's are the best of the 38's, last set made and the most refined. That spring-loaded needle really smooths out the low speed operation. The only downside to them is slide/diaphragm assemblies are hard to come by, they differ from the earlier ones.
Now that I have a later BS34 equipped model and have had the chance to live with those carbs on a daily basis for a couple years, I'm finding I quite like them. As mentioned, the performance is just as good as the 38's even though they're a little smaller carb. I didn't find tuning them for my mods (pods and aftermarket exhaust) any more difficult than tuning the 38's. And also as mentioned, parts are easier to get and cheaper. In particular, manifolds and slide/diaphragm assemblies are cheap.
I didn't find it necessary to shim the BS34 needles like Gary does, probably because I had installed larger mains and pilots for my mods. The bleed-over from them into the midrange pretty much did the same thing as a shim, richened the midrange slightly. I also like the fact that they have an air jet for the pilot circuit you can change. You can use this to fine tune that circuit.
Now that I have a later BS34 equipped model and have had the chance to live with those carbs on a daily basis for a couple years, I'm finding I quite like them. As mentioned, the performance is just as good as the 38's even though they're a little smaller carb. I didn't find tuning them for my mods (pods and aftermarket exhaust) any more difficult than tuning the 38's. And also as mentioned, parts are easier to get and cheaper. In particular, manifolds and slide/diaphragm assemblies are cheap.
I didn't find it necessary to shim the BS34 needles like Gary does, probably because I had installed larger mains and pilots for my mods. The bleed-over from them into the midrange pretty much did the same thing as a shim, richened the midrange slightly. I also like the fact that they have an air jet for the pilot circuit you can change. You can use this to fine tune that circuit.
Question here, considering the XS is a "77"
Do BS34's even fit the 77 air box ?
No. (Actually, I didn't measure, but made assumption.) But, I'm going to be looking into whether or not the BS34 air boxes fit the earlier frame.
Tim L's avatar shows apparently his modified 77, It looks like those are pleated air filters with no airbox and short cone mufflers. Betting the mods are even more than seen.
The picture is my last XS. I sold it then regretted it so much that I built another. Same silencers, VM34 carbs, fram air filters, Heiden tuning electronic ignition. No other real changes, just +.5 rebore and full rebuild of engine. I need to change the avatar picture.
