Piaggio sfera (zip engine) power...

[padly1995]

Hello,
You might remember from few years ago I couldn't figure out why my 1992 Piaggio sfera 50s (same engine as on 1gen zip, air cooled with short case and 10" wheel) has no power.
Scooter was waiting in the garage, but now I pulled it out and decided to try to sort things out...
Problem is that it lacks a bit of power on acceleration and top speed is around 50kph, it should be a bit more than 60kph.

Quick list of things what I did in the past:
Tuned carburator (phbg 17.5mm), spark plug is brown, there is no bogging, it fires right up when cold or hot.
Tryed different roller weights. Stock is 5.2g, I tryed from 3g to 8g and got best resoult with 4g.
Changed exhaust from stock (with alot of holes drilled in it) to stock minarelli exhaust. This also resoulted in a bit of improvement.
Added 5mm bushing to stiff up the clutch counter spring and it improved power a bit, tried to add another bushing and it made power loss.
Installed new belt...
Inspected reed valve and it's reeds, everything else for leaks, changed sprak plug...

So current setup is:
Dellorto PHBG 17.5mm with lawn mower air filter (mallosi mhr filter that it camed with had too much airflow)
New belt 734mm x 17mm -Do any of you know if this is correct size?
New spark plug
Bushing under clutch counter spring
4g roller weight

I attached photo of it's CVT.

Do you know what compression should motor like this have?
Thank you for help

[padly1995]

I HAVE FOUND THE PROBLEM...

Piston is bad, previous owner said he installed new piston, but he didn`t. I don`t know why he even told me that he did, I didn`t even asked him in the first place and price for the scooter was low...
So this is it...

[sc00ter]

Now you have to figure out what caused the piston to go bad. My guess would be air filter. I have no idea why people replace the stock air filter. Depending on how the piston died will give you clues as to what caused it. Scruffs on the exhaust port side or a hole in top of the piston? Also, is it the correct heat range spark plug being used? You mentioned the plug color being correct so that is gonna make it more fun to find out why the piston failed. When my reed cage developed a air leak it seized before I noticed the temp alarm going off! Plug end was bright white and the whole exhaust side of the piston was shot. That was a fun lesson to learn.