ok, so you want to go fast with PX 125 base.
The most powerfull kit sure is the malossi 166.
Polini 177 is the second most powerful one.-
Pinasco is a good touring kit.
DR is a base tuning for the one that want just something more without too much change.
The difference between the two most powerfull kit is this:
Malossi 166 power curve is more high rpm oriented and this has to be taken in consideration for gearing ratio.
Malossi benefits from reed intake.
Polini 177 power is more mid range oriented.
More beef in this range. Good torque. Easier to set up. You can drive longer gear.
I have built engines with both kit and for my personal taste I prefer the polini kit. For me the Polini power range makes more sense for a vespa that has just 4 gears.
The thing is all about feeling, how do you like your engine to be.
I can give you some specification of a Polini 177 engine I did that I
like to drive:
-Cranckshaft longstroke worb5 special lip.
-cluster from PX200 primary 65
-cosa clutch drive 21 or 23 teeth (depends on the exhaust)
-Exhaust RZ right hand
-head gasket 1,5mm (you had to use this with a longstroke. I have tried 1,5mm base gasket. With Polini better to use head gasket)
-Carb. of all the carb I tried the one I prefer is the Keihin PWK28
if you ever going to use one ask me for setting since the good setting for polini 177 is not close to the standard setting.
- Malossi reed (Polini 177 doesn’t get that much better from it, but if you want the most you can get out from a kit this is the way.)
- Crancases ported and inlet port modified to fit reed intake.
- Polini barrel porting modified and piston modified.
- PK modified for PX flywheel.
With a kit like this is of the most importance to set the carburation right if not you are going to size for sure. And you have to set well the ignition at 17. Spark Bosh W3AC or NGK9HS.
If is set up carefully is very rekiable, start at half kick, and vibration is very well controlled.
I drove with this kind of set up for 6000km and 0 problem.
Top speed around 135kmh with 23/65 gearing.
You can get even more power if you use a 30mm carb. But Icompared the 28keihin with the 30 dell’orto and is better keihin.
I used Mikuni tmx 30. A little more power than keihin but Mikuni body much bigger than the keihin and you need some modification to the manifold if you use the malossi reed block.