Contained within the primary drive of the input shaft assembly of your VESPA motor are six pairs of springs. These spring units are arranged so that the smaller springs operate inside the larger springs for a stronger resistance to the forces created within the drive train. If these springs are worn or even broken, acceleration will be interrupted and effected with a jerky action similar to clutch failure. The only remedy is rapid replacement.
The gearboxes of the more performance orientated motor setups are exposed to even higher rates of mechanical erosion. For this reason DRT have high quality primary drive repair kits available that are more suited to the job. These kits include a set of springs that have been strengthened to withstand even the strongest performing motor setups. This makes them the first choice for high-end tuning project, for both powerful road-tunes and maximum power projects. Earlier models of VESPA, tuned with POLINI and PINASCO tuning cylinders can also benefit from this DRT primary drive repair kits, as a timely gearbox update.
Conclusion: The primary drive assembly should be inspected and/ or replaced during any major motor overhaul. Negligence will cost, in time, lots of money and riding fun!
SIP-TIP: Always install and replace ALL of the smaller primary drive components during each major service. The securing plates on both sides of the primary drive, input shaft holding nut, tab washer and also the input shaft needle bearings should all be replaced for save and enduring use of your motor. Last but not least do not forget to order fresh gearbox oil, gaskets and all relevant oil seals!