You can sometimes help by going to a lower pitch and larger diameter, but that is probably not the issue.
More common is to have a tricycle gear model with the nosegear a bit too short relative to the mains and/or the main wheels too far back. Then when the elevator has enough authority to rotate the nose up the plane over-rotates into a stall.
This was an issue with the plane in my avatar (mains too far back) requiring me to extend the nose strut by over 1 inch.
For hand launch the issue is normally just tossing it too much nose-high. Aim at the ground about 30 to 50 yards away.