Translations:KAVAN FS400AR - Instruction manual/37/en

From KAVAN RC Wiki

Instructions for Valve Adjustment and Tool Kit

Valve clearances are correctly set before any KAVAN four stroke engine leaves the factory. In normal use, the valve clearances are not necessary to adjust until extended running time of the FS 400. However, in case of loss of power after extended running time or when the related parts are replaced due to crash, etc., valve clearances should be checked and adjusted.
Additionally, we suggest that after proper break-in of the FS 400 carefully check to ensure that the valve clearances are correctly set.

Note: ONLY check and re-set the valve clearances when the engine is cold.
Important: Valve clearances that are too small may cause difficulty in starting your FS 400AR because the valve will not be able to close properly, while valve clearances that are too great may cause loss of power because the valve will not be able to open sufficiently.