Carb compatability

[thebigfootman]

I have a 1974 xs650 that has been revving up when given throttle and then dying to the point where it is un-rideable. The bike still starts on first kick and idles perfectly. Furthermore the left spark plug fouls within a few start-ups. After investigating the carbs (keihin PWK 28') which were on the bike with purchase I found huge gaps in the rubber boot as well as a silver extender piece between engine and boot which I am unfamiliar with.

After reading the forums it seems that this carb is both finicky and far more carb than my bike requires, as well as potentially poor construction. I am thinking of buying either used Mikuni CV carbs (34 or 38?) or a new set of VM's, but cant figure out compatibility. Can I put a set of xs650 81's on my '74? Should I try to find BS34 or BS38s? Or, should I keep tinkering with these PWKs?

Any advice would be much appreciated!

Kyle

 

[5twins]

My advice would be to ditch the Pukes (yes, they deserve the nickname, lol). You may never sort them and it may not even be possible due to, as you mentioned, the poor build quality. Literally, some are just screwed up inside.

You can use either the BS34s or the 38s. I would latch onto whatever was the best deal you run across. With the 38s, I would recommend a '76 or newer linked set, not any of the '75 or older separate carb sets. For the 34s, they're all about the same but the 1st year edition, 1980, was a bit oddball. They had brass floats for that one year only and they differ from the BS38 ones so replacements may be difficult to find. Yamaha did still have them but at $35 to $40 each. If I had a choice between '80 BS34s or a newer set, I would choose the newer ones.

 

[thebigfootman]

Thanks for the advice. Sucks about these PWKs.