Modern Vespa

My goal is to make it stronger up the hills, more accelration and top speed 65-70 km/h (40mph).
I will not go for long stroke 53mm crank and 125-130cc.

I have a Swedish imoprted vespa 50 smallframe 1966 doing 30km/h with following

specification:
50cc
10" wheels
Banana exhaust
Crankshaft (with minimal possible cavity, was to made them slower here)
Primary gear: 14/69-4,93 (also different on swedish imported than european 18/67)
3 gears
16/10 carburettor

Is following a ok setup?
75cc D.R Formula
4 gears
Carb 19/19 or 16/16
Primary 18/67: 3.72
Race crank 20mm spigot
Electronic ignition

I am unsure regarding primary gears. Maybe I would like to step up to 85 or 102cc in the future (I think 18/67 is good between 50-75cc). Would be nice to do that whitout splitting the engine again and changing both primarys.
I could buy a 24/72:3.0 kit which gives me possibility to change the small cog separately between
21/72:3.54, 22/72:3.27, 23/72:3.13, 24/72:3.0, 25/72:2.88

Can 50-75cc with primary 21/72:3.54 pull my weight 95kg (213lbs)

If I buy 18/67:3.72 there is only one more option and its 19/67:3.52

Wow, that model is really slow. Since you're changing everything I would upgrade to the 102cc kit now. Why do it later, when you think you might need it now? Then you can target the gearing to best suit that particular set up.

Thank you for your answer! I want to keep it quiet and top speed is not very important in the city. I also have a 125 primvera for more speed. This one is not allowed to drive faster so want to keep a low profile. 75cc feels like a good start maybe 85cc

Ok, I get keeping it quiet. In my experience keeping it quiet is not really related to displacement (75cc or 125) but exhaust, air filter and state of tune. So with more displacement and longer gears the scoot will have to work less to make the same amount of power. To me that equates to more "quite".

For quiet I would be looking first at my exhaust and making sure it's in really good shape and buying a kit that it tuned for low revs/torque like a DR.

Yes I don't argue with that. You are correct. Just don't want to tune it to much, if I get stopped it is going to give me more problems with a more powered up engine. I have been more "reckless"

Yeah, no argument here just decoding your logic. It sounds like have already decided to stay at 75cc. Then you really just need primary gearing advice but I'm not that familiar with short stroke setups and nobody I know is. Most people I know would go to 130+ if the crank was coming out.

Yes, for this vespa I do not want more. Guess I have to take some chances if nobody knows Thanks for your advices

The SIP catalogue does give recommendations for each primaries application. Just get something strait cut and go for it.