Hi, does anyone happen to know if you can run 16% Nitro in a Novarossi .21 Keep on engine? I've read before you can adjust with shim removal, but I'm not sure how many need to be removed. I know the Mephisto engine includes a 28038 button head for running 16% and recommends purchasing a 28025 button head for running 25%. I'm wondering if the same applies to the Keep On engine which comes with a 28025 button head. Not sure what to do since they banned 25% nitro here in the EU.