All the stuff above yet here are some more 2 cent suggestions.

11-6 on a sport 40 is a bit much. 11-5 may help, but I suggest an 11-4 or 10-5.

Grass can well slow a big airplane down. Grass can be a deceiver.

You say the machine weighs 6#. YOU DON'T SAY what the wing area is. [:-] If a 6# model has less than 600 sq.inches w-a, then you may have a low-power problem. If the wing area is 700 sq. inches, it should leap right off.

And as pointed out above, be sure the airframe is sitting level. Nose down provides negative lift to hold you down. Too much nose up will normally either drag you down or leap off before flight speed is attained. Then you will bump the nose gear first when you land because it's difficult to land with the nose so high. Bend that main gear down using both weels at once. Set it level. Almost every day at the field, I see those problems but the self-ordained experts don't want any advice from the old flart that never has such trouble. so I keep my mouth shut with a smile.

Good luck.