Serpento COBRA Manual De Usuario página 90

Fuel
Please use leadless gasoline. If slight explosion sound comes from the engine, the possible cause might be improper using of general fuel.
thus places replace the fuel.
Note: Using leadless gasoline can prolong the lifetime of the spark plug.
Engine Oil
Use of high quality 4-stroke engine oil would extend the lifetime of the engine. Grade SE or SD engine oil in API method is recommended,
whose viscosity is SAElOW-40. If this oil is not available, please purchase appropriate substitute according to the data listed below.
24