I think your question is answered above, but as far as you not getting the rpm is concerned, perhaps you are on the bit of the large size with your 11 X 6. Drop down a bit to to a 11X5 or 10X7 and it should spool up better. Different prop manufacturers will give you different RPMs as well. I prefer APC, and others may like different brands. Also if it is new, your engine may not have broken in yet. Dont run it too rich. Most tachometers are accurate and a wise investment. You may wish to invest in one or ask for one for Birthday or fathers day.