PK50 XL Cylinder kit upgrade 75cc

Hi All

I just need some advice as I am completely new (first scooter with no prior experience) to all of this.

I have a PK50 XL all original but using a 16.15f carb and would like to upgrade the cylinder so that I can keep up with traffic at about 40mph as opposed to the current 25mph I currently get.

I don't want to spend loads of money and make loads of changes so therefore have decided that a 75cc kit would be suitable. Do i just simply swap the cylinder kit for the old one or do I need to make any other changes?

In other words will the kit upgrade work without having to change anything else.

Please remember I'm just looking for a bit of extra speed not looking for major performance upgrade.



I have upgraded my 50 special with a Polini 85, new exhaust (banana) and a 19/19 Carb. The speed increase over the original setup is noticeable - my Scooter now does 75 kph easy and will do 60 kph with 2 people riding uphill so power and acceleration are top now. Previously the scooter did about 40 kph. First thing I noticed after the upgrade is that my clutch started slipping which I remedied by installing a new Malossi spring and new clutch friction plates (SIP article 52165210). This is a pretty easy installation assuming you have a clutch puller and ideally a clutch stopper. I plan on complete engine revision (I am having some gear shifting issues) over the winter at which time I will change to a 3.0 primary - rationale being that the engine will not have to rev as high as with the current setup. Top speed will go up too, but the scooter is a bit dodgy above 60 kph so I don't imagine driving that fast.

A new cylinder only increases power (e.g. "torque".
With the more of torque, you only get a very limited increase of speed... (75 ccm means only 2-4 mph more, compared with the original engine with 50 ccm).
You need to change the primary transmission.
(Imagine a very strong body builder, but who has only short legs.. he will not run fast! Got it?)

For a Vespa changing the primary trasnmission means opening the engine case completely.
A lot of work and nothing for a rookie regarding such surgery

Also, for a 75 cmm cylinder it is recommended that you mount a 16/16 carburetor as a minimum.
In most of the cases you will not get the 16/15F to run properly in all situations (the reason ist this carb is a choked version of th e16/16 to reduce emissions according to legal regulations).




I am thinking of getting the Polini 85cc for my PK 50 xl as well...

My problem is that it is too many options, and I am thinking of the same as you: Cylinder, carburator, + jets clutch, and gear. I already have the LeoVince exhaust.

Do you have any recommendations for what I should choose?