V Thunder Manual: Vento

A: The manual identifies two causes: 1) Leaking exhaust gasket (Replace the copper ring). 2) Lean pilot circuit (Turn air screw in 1/4 turn).

If you are looking for a service or owner's manual, you can find them on these platforms: Vento V Thunder Manual

The manual strictly warns against using automotive motor oil with "friction modifiers" as they will cause the wet clutch to slip. A: The manual identifies two causes: 1) Leaking