Tuning a 1966 125 super

Last year I bought a 1966 Vespa 125 super. It’s an original dutch Vespa and I’m the third owner. She was totally worn out but chassis was ok and she was complete.  Because a 125 super isn’t a collectors item I decided that the lady had to be tuned a bit. The catalog of SIP is awesome and helped a lot, but after a (long) period of studying and selecting parts I found out that I was going to end up with a racer…and not with a scooter that is to be used as frequently as possible  Plus, it was becoming wel over budget…(polini 177, racecrank, 24/24SI, sip road, very long DRT clutch, gears and primarydrive, modified crankcase, etc., etc.).

 So, downtuning the list I finally came up with a set-up that could create a daily driver with some more power and rev’s to get me out of situations as on a highway within to trucks at 80 km/h. And, also important, I can do it in several steps: first all the necessary parts (as bearings etc.) and parts in the engine (casing is split) and somewhat later, a stage 2 tuning: 177 cc, bigger carb etc. I sure need to split the costs. I hope some of you can give me some advice or maybe have some tips.


In the old days I had a Honda MB5. Adding a sport exhaust to the standard cylinder really made a difference. That’s where I want to start with the old lady: a SIP road exhaust in combination with the original cylinder and piston and do some oldscool tuning: flowing the piston and all the ports and modify the exhaust port (trapezium as in the SIP catalog described) . I want to increase and flow the inlet: 2+2 mm front and back and, carefully, 0.5mm sideways.  The ports in the crankcases can be modified a little without welding extra material. (I even can make a small third port so, for stage 2, a 177cc with three instead of two ports is an option). Because of the fact that a racing crank has a very long inletperiod (high revving engine) I choose an original crank and optimize the flow a little by polishing. The 20/17 carb can be modified just a little to deliver some more mixture. In combination with a polini177 the SI 24/24 is the best option (they say)  but I’m not sure the 24/24 will do fine on a slightly tuned 125 cc. (difficult to adjust?). Maybe a 20/20? How is 20/20 on 177cc? Or just start with the 20/17? and later the 24/24 in combination with 177 cc. Because I need a new clutch I want to build a clutch with original dimensions (108/96) but with sport plates and reinforced springs. I think (hope) the extra power and higher rev’s will allow a DRT 23T clutch gear (instead the original 22T) but DRT 23T fits only super2 and not super1. because of the baseplate. An orginal 125 super-1 baseplate is 1.5 mm higher than a super-2.Will a spacer fix the problem? Or thicker plates?

 Hopefully someone tuned a 125 super or 150 super before and can help me with his experience.

Thanks in advance.