for Vespa 160GS/?180SSfor Si 27.23Grade A – original restorationProduct descriptionOn the SI carburettors, the choice of the idle jet primarily affects the lower and middle rev range. Each of the jets are marked with two numbers, the relationship between which states the actual jet size. E.g. 50/120 ? 2,4. In general, the following applies: The smaller the value the thicker the jet. And/or the bigger the calculated ratio of the idle jet, the leaner the scooter will run with moderate revs. This is important when undertaking long tours when it is necessary to drive in the difficult half throttle range for long periods. Our range includes several DELL’ORTO idle jets from 55/100 (1.82) to 42/160 (3.81). It isn’t worthpenny pinchingand using reproductions. Anyone who has tuned a carburettor before and wasn’t able to rely on the regular sizes will know what we are talking about. Conclusion: Seizing at half throttle? It would never have happened with the right idle jet! -TIP: The best idea