v90 4-speed

[byron]

I have been asked to fit a 4 speed box into a vespa 90 engine.
it has a DR 135 kit fitted and is screaming its nuts off, to the point of holing the piston...

so what box is needed ? I was thinking primmy 125
it has standard 19mm carb, and an expansion pipe of some sort.

does anything else need changing ? clutch ? primary drive etc..??

thanks

[BruLi230]

You don't necessarily need a 4-speed box, tho a Primmy one will go in.
Upgrade to straight-cut primary drive, clutch, etc.
Bigger carb, race crank & porting &will make a difference too:-)

[wack 63]

Any 4 speed box(all the same) and matching selector will be ok ,it is just the primaries that alter the overall ratio.Try here http://www.scooterhelp.com/tuning/vespa ... .calc.html or check out Norrie Kerrs tuning book

[Juan]

Use standard 125 primaries and if it were me then I'd also use a Polini clutch spring and either Newfren or Surflex 3 plates seeing as you're in there anyway.

[soosh]

Use standard 125 primaries and if it were me then I'd also use a Polini clutch spring and either Newfren or Surflex 3 plates seeing as you're in there anyway.

Can you still get the Polini spring? I mean the square coil type? They were the nuts.