Main jets by 101 Octane for original carburettors, M4 thread. Restricted E2 engines often have jets that are too small. Especially after installing 70 or 80cc cylinders. Recommended when fitting a sports exhaust or 70cc cylinder. An increase of 10-15% is recommended for 70cc or 80cc cylinders. Check plug to see how the mixture is running. Suitable for 4-stroke scooters with GY6 139QMB/QMA engines and all Naraku 4-stroke carburettors. Not suitable for 4-stroke models of the Kymco Agility 50 and Super 8, or on Yager GT50 models with original carbs. Relevant size of main jet supplied.