Just wanted to comment on spitting fuel out of head button. I own 3 GRP Ninjas. Two are .28 and one is a .21 . Two of the engines would only use OS plugs and ninja plugs with no leaking. The other one would only use Ninja plugs, all OS plugs would leak . My buddy I race with has a Ninja .28, and his leaks with OS plugs but not with Ninja plugs. After this many GRP engines, and this many issues, I figure there has to be a factory defect with the head button. Its a good thing I love the way they run , and the 10 gallons I got on the .21.