Kostas, I agree with some of the others: the 11 x 6 APC prop is a bit too much for the poor old .40 LA. An MA 11 x 6 would be a better bet (1bout another 1000 rpm), or maybe an MA 11 x 5 or an APC 11 x 4. Depending on the airframe, an APC 10 x 6 might work too.

It's unlikely to be doing more than about 9 and a half to 10 grand with the APC 11 x 6, which will badly hurt fuel draw.