The US distributors (Sudco, CPW, etc.) and Mikuni America do not see fit to make TM34 4-stroke pumpers available to us. The TM36/68 is available here, I love mine, but if you're not ready to do some serious fabrication, don't even think about it. The 34's are available in Europe, and Topham's makes a flat-out beautiful kit for the XS650. It may look pricey, but I can tell you from experience that you won't get the job done tuning and modding a pair of TM36/68's for less. See
www.mikuni-topham.de .
I've acquired some 33 mm. Mikuni 4-stroke flat slide pumpers, one bank of two and one bank of 4, and I'll be playing with them as time allows.They're similar to the TM33/8012 pumpers but show minor variations from those and from each other. They have real promise; for one thing the throttle shafts are mounted forward of the slide towers, allowing the use of extended mounts.