I have one too. I only ran 2 gallons in it, and it ws going btter and better. they say true, 14X6 or 15X4. I used 15X6 once, but rp was low, thrust was the same, that on 14X6.
get this engine. u'll be happy. it starts wonderfully. I newer used el starter, but maximum 3 flicks with finger,(but it shoots propeller heavely. use something heavy lether or something like it) and it runs.