Maybe you are trying to run too much nitro in the ST.61? Carb adjustment issues some people have can be solved with some reading/research.

OS and ST both, as well as others, make a current .75. The .61 OS SFs, FSRs and Webra Speeds are all over the www classifieds and a big auction site right now. Often I see RFs, HBs, HPs, etc. too. You gotta be on the lookout to catch one. Can't just visit every week or so unless you are Irish.

Almost any engine can be made to work with a faired/internal pipe. You might have to improvise in the construction phase instead of following the plan precisely. Custom headers can be obtained or self made for side exhaust engines as well as rear exhaust engines. Mousse can mufflers that have a wide boosted rpm band and are shorter than standard tuned pipes can be made or bought. There are some mini pipes available (MVVS) too.

Terry in LP