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read the "read first" post at top of forum. we need much more info than what you have given...but just a guess...get a 15 P 4 blade.. it is kind of a trade off to get more hole shot you usually lose some top end...you can get a vented prop, they help also trim tabs help a bunch for coming out of the hole. your answer could be more than just repropping.
diameter is not important, but should be stamped on the prop next to the pitch, you are guessing at the pitch,,,, what makes you think it is a 21 pitch prop??? and again read the "read first" post at top of forum, still need much more info to help you out.
