Vespa PK100

1_Vespa PK100 S

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I recently acquired this Vespa PK100 S in a TM auction.

The seller had purchased it from the previous owner who had supplied the following information with it:

Vespacross PK130s dirt scoot

A little different to your normal vespa. I built this thing for racing small bikes where they shouldnt be.
Have done a few races and had my fun, time for someone elses turn, or someone elses garage ornament, or use the parts in a road going vespa small frame. It has a a 4 speed 130cc smally engine.
The scoot originally started life as a late 90s/ early 2000s (not to sure) PK100S. I brought it missing a few body parts so filed in all the indicator holes and head lamp and made a dirt scoot.
Raced at the famous QCR dirtmasters in 2020 and the recent 2022 Garlicmasters where it developed a slipping clutch issue. was a new clutch when built but possibly needs an uprated spring to cope with the increased power.
The engine is a 4 speed PK small frame engine with the larger taper and stronger crank with a proper little end bearing not bronze bush like earlier smallies.
I installed a 130cc smallframe cylinder and head.

The port timings have been improved but “top and tailing” the cylinder. Correct calculations were used and i opted for a 3.4mm base riser and had the same thickness machined off the top of the cylinder / barrel.
The exhaust port height was also altered. Current timings and engine details:

Vespa timings

Pk130, top&tail with 3.4mm spacer
Inlet Starts closing -25 ATDC
Inlet Closed – 55 ATDC
Inlet Starts opening -110 BTDC
Ex port starts open- 90 ATDC Ex port fully open- 150 ATDC
Tran port starts open- 119 ATDC
Tran port fully open- 180 BDC
Trans duration – 125 degree
Exh duration – 180 degrees
Current squish without packer and without head gasket = 1.15-1.2mm

Has a polini banana exhaust which sounds awesome and a polini air intake. Carb is a dellorto 19/19.
The scoot has pretty much brand new knobbly tyres and new foldable CNC leavers. He had a slim seat installed and 1/4 turn racing throttle instead of the vespa cruise control spec clunky thing.
As mentioned earlier the clutch needs replacing and the steering head bearings are also a bit clunky and likely need doing.

I have some plans for this over the winter hopefully to race it at the next Burt Munro.