As Roniel stated that the HeadClearance to Nitro maybe incorrect. I personally would add another .10 shim and see how it goes provided that you are going to run the same fuel. I have yet to see a motor blown up when it's too rich that's not to say running too rich does not have it's own share of problems. Too lean is as bad as it gets so you NEED to be very careful when turning that needle clockwise.
If you google it Parris Racing had some great articles on engine tuning. TO me this guy is the grand Daddy of nitro tuning. He explains what to look for in the plugs, tuning bottom and top end, even fuel care.
Hope that provides some direction