Modern Vespa

Hi All
I've Just bought a px 125 disc ( engine completely rebuilt by retrospective scooters only 600 miles ago) with the eventual aim of attaching a sidecar.(inspired by Charlieman 22 although it won't be a leaner ).
Anyway to start with I intend to fit a polini box and do a bit of tuning with the standard barrel aiming for a torque monster, moving on to a kit later( vmc?).
Need a set of main jets to tune the scoot for the polini box but not sure what range I need.
Any advice would be welcomed.
Cheers Andy

Thanks ferris wolf, box and a set of jets are on their way, will update you all on my progress.
Any suggestions for tuning the cylinder?
I have read loads on this brill forum, but not sure which mods would get the results ( if any) I'm after i.e. torque.
Thanks again.

Sounds like fun, ( i know everybody thinks im nuts) but two reasons for the sidecar, 1 ive never driven one and at the tender age of 66 i want to complete my vehicle education and
2 one of my grand daughters is disabled but loves motors and the sidecar is the only way to go.
I understand that kitting is the only way to go eventually but I'd like to have a go at tuning the 125 more for experience than anything else so what can I do to the std motor for more torque, then i'll be back to find out which kit is going to give me torquiest machine.

Can I ask,Feriswolf, what kit you have on your scoot, planning ahead as to what direction I'll be going going in later re cylinders, quite like the look of the vmc stevio but as always open to suggestions from all you knowledgeable folk.

Just found/read your thread re your build, Did you try the polinl head and up gear?
If so was it worthwhile?

Andy - couple thoughts from a fellow sidecar enthusiast...
First - boys over at Retrospective know their stuff - so expect the bottom is is solid.
No reason to split cases - cylinder will be plug and play.
Perhaps that was already clear.

On cylinders - thump is good - when pulling a sidecar up the A502.
From a bang for buck - you are on the right track.
Cylinder kit and exhaust are by far the biggest - especially in combo.
Given you are starting with a 125 - that cylinder will be a game changer.

There was a time where the options were:
1. Improved iron cylinders like Polini
2. High end nikasil lined cylinders like Malossi
3. Cheaply made, big tolerance, fairly low quality options like DR.

While #2, remains - number 1 and 3 merged - to our benefit.
Today you can pick up either a BGM (German made, tight tolerance, great for your application) or VMC (little cheaper - little more variation from product to product).
Both are aluminum cylinders with the nicasil liner.

Why do you want a nikasil lined cylinder?
Well - cause they are much less likely to seize.
They take heat better and...
Seizing is, well, really unpleasant...

Have a look at those two.
Plug and play - I would probably grab the BGM (which I have done myself in the past).
You will be knocked out in comparison to what you are running now.
Reliable and solid.

either a BGM (German made. . . . )

Thank you all for your input, its much appreciated,
First up, fit the polini box exhaust and set that up right, going to do a little tuning on the standard cylinder just to practice working on a 2 stroke,.
Going to go with the scooter classics article as a basis, raise the barrel, skim the head, a little work on the exhaust port, (slightly wider, 1mm each side and a 1mm raise) then practise jetting it so that when I come to the kit I have half an idea what im up to.
If I knacker the std cylinder on the way then gives me an excuse to get the kit a little earlier.
Will definately keep you updated because I'm gonna need some hand holding during all of this.
And Charlieman, if I ever win the lottery I'm paying you to build me a leaner

Unless you have a local source setup to skim a head already, I was looking at $100 -$150 to get one skimmed. About an hour of time to get head fixtured level. One reason I went to a center mount plug. Machine shop can fixture it on my piston stop and take some off using a lathe.

You can get cylinder skimmed also. Shop can clamp on base for centering and level or put it in a lathe and take some off.

Check around maybe someone has a good 150 cylinder and piston laying around that just needs rings. Maybe someone has a DR177 or something laying around you could get cheap.

You can hand lap material off head using wet and dry sandpaper and a piece of glass to keep things flat.


I have a guy who runs a local garage who normally does car stuff ( he skimmed an old landrover head to raise its compression for an lpg conversion I was running and also modified some mobility scooter stuff for me to fit into a childs car I built) so he's well use to me popping in with unusual requests but if the skim is too expensive then the kit idea will be brought forward.
Not too worried about money as this project will be staying with me until the kids get it in my will. , but on the other hand I do like getting my moneys worth (who said tight git) and I like working on vehicles and getting the hands dirty so modifying stuff although new for me on a 2 stroke is something I'm looking forward to.

Stand corrected.
German sold...

Asian made most probably…

Next problem, having troublre refitting the bolt that holds the exhaust to the bottom of the engine , the bolt just will not engage with the captive nut, any 'tricks of the trade' that will help me
Thank You.

Center the nut with a screwdriver and wedge a little piece of cardboard in there to keep it from dancing.

Next problem, having troublre refitting the bolt that holds the exhaust to the bottom of the engine , the bolt just will not engage with the captive nut, any 'tricks of the trade' that will help me
Thank You.

Thanks RayI've tried that , it seems to me that although the bolt is entering the nut they're at a slight angle to each otherand because the bracket is a snug fit around the boss I haven't got any wiggle room.
A couple of ideas come to mind,
1)Open out the bolt hole in the bracket and the boss to give me some rattling room and
2) open out the hole in the boss a couple of mm.
Any views on the above(' Dont be a twat' is acceptable as a comment )

Next problem, having troublre refitting the bolt that holds the exhaust to the bottom of the engine , the bolt just will not engage with the captive nut, any 'tricks of the trade' that will help me
Thank You.

Thanks RayI've tried that , it seems to me that although the bolt is entering the nut they're at a slight angle to each otherand because the bracket is a snug fit around the boss I haven't got any wiggle room.
A couple of ideas come to mind,
1)Open out the bolt hole in the bracket and the boss to give me some rattling room and
2) open out the hole in the boss a couple of mm.
Any views on the above(' Dont be a twat' is acceptable as a comment )

Adjust hole size to remove strain causing angle.
Proud not ashamed of a well fit part.

I read it as the bolt being forced to sit at a slight angle, caused by misalignment of three parts, the two holes on the respective ears of the exhaust, and the swing arm hole.
I assumed what the PO was stating was, if he relieved the top of the hole in one of the ears, he could get ghe bolt to go through the swing arm and align with the other ear, without angle or tension.

Correct?