The flywheel originating from the Vespa PK50/XL/HP, with its low weight of only 1 kg is also capable of accelerating every other Vespa model with electronic ignition.
The HP4 flywheel for the PK/XL and PX models is supplied in two versions to fit to the two different types of crankshaft profile. The version for the smaller 19-20 mm cone is also popular when upgrading an earlier small-frame motor to electronic ignition. The fan part of the flywheel is made of plastic and can be removed. The relatively light weight (1kg), as opposed to an original flywheel (up to 3kg), allows a noticeably more direct throttle response and higher engine revolution range. You can even resuscitate original cylinders with this flywheel.
The diameter and size of the fan part of the flywheel is considerably smaller then with the original PX flywheel and therefore less suited for the next Saharan safari.
Since the motor will become somewhat more aggressive through use of this flywheel please pay attention to the following points:
- make sure of the correct size flywheel corresponding to your crankshaft employed
- order the stator pack-up plate spacer (art. no. 50011300) to avoid misalignment of the pickup
Conclusion: An enormous tuning effect for minimal effort. Ideal for street racers.
1000g, balaned, cone depending on version 19/20 or 20/20 - 24/25mm, removable fan
SIP-TIP: If you experience misfiring after fitting HP4/PK flywheel to your PX motor this usually means that the stator-plate and flywheel are misaligned. The stator pack-up plate spacer solves this problem by raising the profile of the stator-plate back into alignment with the flywheel. For electronic ignition conversions also order the CDI unit, voltage regulator, wiring loom and 12V bulbs for all lamps.
SIP community user “CHRIS” about part no. 50010000: “Mate!!! The revs shoot straight up with this item, its the business. You could already consider that your road-going Vespa has mutated to a full blown racer :-). So, whoever is after a not so obvious tuning method, I can recommend this gem. (not for use by Sunday riders, due to high danger of wheelies)”