Always add air when changing jet, more gas more air more power.
Back in Stock Keihen 95 jet fits 139QMB carb best used with air filter and all other upgrades.
95 main jet for 139QMB carbs. This is the only size we will carry for now until we find a better one for exhaust and air filter upgardes.
We have found our scooters have 85 jet so going up to 95 rounds out an exhaust upgrade as well as cylinder.
These are Kehin jets and not chinese jets, we went out and got the real thing because of problems with jets and quality from jets from chinese scooter distributors.
Adding a high performance air filter and larger jet gets you more air more gas more power. The Uni Filter is the best for this purpose.
When doing cylinder upgrade changing to larger jet gets the best performance plus adding a pipe really completes upgrade.