To kobago: thanks for your reply. I think the pressure in the tank is OK since I de-pressurized the tank after every flight and re-fuel it just before my competion turn.

To James: I don't understand why you mentioned that "the DZ's are tuned slightly richer on a day to day basis"? Is it a MUST-BE procedure or something else? And by the way, do you have any suggestion in the selection of prop? will lower pitch (or smaller diameter) prop will solve this problem?