BS34s not the same?

[volvit]

Hello all. We'll I finally unloaded another project and now I have a chance to get my 81 XS400. I've been chasing a flooding issue and determined the needle in the bowl was traveling to far even though the float levels were within spec. Long story short, float post broken, need new carb. I picked up a set from a 77 xs400 off ebay, chancy I know, but they arrived and I couldn't be happier with the condition. I tore them down and the only thing I found to need immediate attention is one side/diaphragm. I figured I could swap parts needed from my original 81 carbs. Not quite, the slides on the 81 are 29mm while the 77's are 28mm. From my reading, I was under the assumption that all these BS34 carbs are the same, just jetted differently. Am I missing something here? If this is true, is one set better than the other? Thanks.

 

[Robsteeler66]

Hopefully, XSChris will see your post. He'll know.

 

[xschris]

77-79 carb slides/diaphragms and 80-82 slides are not the same. There are many other parts also that won't swap. Bowls, float valves, tops, slide springs and idle mix screws. One thing to be careful of with the 77-79 carbs is the idle mix screws are not broken off in the carb bodies. If they are good, just be sure to be gentle when adjusting them. Don't tighten them down hard when setting them for turns out.

 

[volvit]

Everything came apart in one piece, so I'm good to go there. Does one model have an advantage over the other?

 

[xschris]

With these, no not really. The 80-82 carbs have easier to obtain parts. The 77-79 are more likely to have idle mix screws break in them.