Vespa V50 Series 1 – a closer look on tuning with Polini Racing 75 cc kit (item number 7675516)

The first Series of the Vespa V50 differs in some details to the later version that is much more common.

The early V50’s for instance have the frame numbers V5A1*1001* up to *92877 and V5SA1*1001* up to *15325*.

Differences of the first Series are the suspension, the fixing of the rear brake plate with M6 studs, the three speed gear box, the 9 inch wheels or the shorter wheelbase. There are lots of small differences and unique is the engine as well.

If it comes to give this a little more power, there are some things that should be considered.

The original engine put out slightly more than one horse power (1.2 hp to be specific). This in conjunction with a very tall primary drive ratio of 3.72 and a very big gap between second and third gear make this engine anything else than a good performer.

So if you want to use the first Series for anything else than collecting dust, fitting a larger cc cylinder kit is very advisable.

The cylinder neck and the engine casings are smaller on the V50 1. than on the later models. This makes fitting of all the cylinder kits impossible. To cure this problem we have a ready machined cylinder kit on offer.

It’s the Polini 75cc kit in the so called Racing trim. With a good power band and a maximum power of 4 hp it is the right choice to pull the tall gearing. The good power band even copes with the large between 2^nd and 3^rd gear.

The cylinder base is machined to fit to the smaller diameter at the casings

The cylinder base is machined to fit to the smaller diameter at the casings

Included to our cylinder kit is the speed nut M6 for fixing the flywheel cowl and cylinder cowl. This is necessary because the mounting points are on a slightly different place on the first Series.

Polini recommends a ignition timing setting of 17° for this kit. If you are still using the contact breaker ignition system you can use a testing lamp to set the ignition timing at 1.4mm before to dead centre.

Depending on the exhaust used and if a racing crankshaft has been fitted you should adjust your main jet accordingly to it. The fitting instruction of Polini says a main jet of 66-68 for the SHB 16 is right. We found that a main jet between 74-84 is right.

These carb kits are a good choice for the cylinder kit:

SHB 16/16

SHB 19/19

If you have to give the engine a going over anyway to replace the usual suspects like wear & tear parts as the gear selector, gaskets and oil seals, you should think about fitting a Rracing crankshaft …

as well as a short 3rd gear

The racing crankshaft gives a better filling and hance a higher torque figure. The shorter third gear gives a better gap between 2nd and 3rd gear and makes steadier accelerating and riding two up much more fun.