Thanks guys. I wasn't too sure. It seams funny how it doesn't seam to go much faster even tho I give it more throttle. I'm guessing here it is the same as a car going up a hill in a particular gear. If that gear is too high , ie 4th , even if you push the pedal further down , it doesn't go up faster........select a higher gear ie 2 or 3 , and your away. Would a similar thing be going on here with my prop? Maybe I will drop down again to the 12x6 or even an 11x7. Yes I am basing this on what I see. Up until this point I was flying a 40 size boomerang , fitted with a OS 55AX , with and 11x6 prop. I got used to that speed , and this plane seams to go slower........at full stick , for me it's like 1/2 the speed of my boomerang , and I worry about stall. At present the 13x6 is flat out at 1/2 power and anything from 1/2 up doesn't seem to have much effect at all......yet when I ground the aircraft and check the carb barrel , it seams to open and close as it should Ie at 1/2 power it opens 1/2 way and at full power it opens fully. However , when in the air 1/2 to full seams to do nothing , which makes me suspect I have done something wrong with prop selection. If not the prop , what else could cause this? Cheers