My is Suzuki CS50 1982, that my scooter barley reach 31.4ish mph. I did order a performance air filter, high flow exhaust and upgrade main jet. But the engine sputter at 80% to 100% throttle. It sound like too much fuel or too much air gone in the piston unburn some fuel. Plan B remove the air filter and refit standard air filter. Test at 80% throttle no splutter but at 90 to 100% start to splutter! Plan C remove the main jet which is 90, downgrade to 88. I live 40 feet from the sea level. It runs but same splutter but not too bad as the 90 main jet at 90% throttle. Plan D return the original 85 main jet it runs lovely to 100% throttle! So why did they sell main jet large size with more fuel but it can't keep it smooth at high rev like 80 to 100% on throttle without splutter? I felt that I have waste my time! Next time I will not bother trying to change the main jet and high performance air filter just buy a bigger engine!
You cant see it like that because firstly you have no clue how it works, every bike / scooter will require different jetting you buy sets and u tune right, in your case it just had big jet from the factory so it didnt needed upjetting, doesnt mean that they are stupid because they sell bigger jets. Different setups require different adjusting etc etc there is so much to it.
