Modern Vespa

When read some of the threads in here you see different information related to parts used and so on.
My scooter has some issues, not big, but there are somethings like sound when acleration, sound in muffler when declaration, idle speed cold and some other things related to the instrument panel.
One of the last owners did buy some parts and change related to the variator and air filter that doesn't have same measurement as OEM
- Drive belt change to Malossi X-K L=835 - W=22,5 - H=14mm
(Original drive belt is L=835 - W=21,5 - H=13mm)
- Air filter element change to Malossi Double red sponge
- Roller's 21 x 17 x 13,6g (same as original)

So will the drive belt mounted with other measurements do anything related to the behavior of the scooter?
will the air filter element do anything with the behavior of the scooter?

I will do some demounting this winter (of season) to see if there is need to do something with the variator parts, like missing grease or other things.
Checking the electric cluster at the instrument panel.
check the valve clearance since my idle is slow when scooter is cold

The air filter will have no affect good or bad (assuming it's in good condition and correctly oiled).

idle slow when cold: how slow? do you know the rpm? are you sure there's a problem?

the rollers: check them for flat spots. some people claim the malossi get flat spots quicker than oem. flat spots can cause a rattle.

belt: the slight change in dimensions does change the acceleration.

sound in muffler? what sound? maybe the exhaust bushing needs replacing? part number 8263885

Idle slow when cold = check the idle air bypass passage in the throttle body is squeaky clean.

https://cheekythoma3.wixsite.com/itsme/idle