your blowing plugs because of the tune, i suggest you go get it tuned professionally after run in! and i expect your LHS will tell you what i have told you
i expect you spent a fair bit of coin! when in reality you should not have, do not get me wrong hyper 7's are good but you could have bought something better for roughly the same price! i have delt with them (.21 engine as standard) and it was good but over priced! not long after selling the hyper (the value dropped dramatically and i got nearly half what i paid for it) i decided to try something different, i came across thunder tiger...
i still have one, although its awaiting rebirth when i can find the time and money... if you ever want to go a race motor (bump box required) i have a ported samurai .21 which i do not expect to ever use! as i no longer have plans on racing but bashing... i can do a good price on it
MOTOXXX, from photos it looks small but in-fact its fairly big! its 1/8th scale! put it up against a 1/10th buggy and you can see what i mean