Consider reinforcing the motor box on all your ARFs. I use 3/8 basswood triangle stock on all joints in front of the front bulkhead, & 1/4 in triangle stock where the motor box intersects any other bulkheads. For example, I did this on a GP Patty & ended up withe a 16 lb plane. Also, did it on my EF 87" Yak & it still came in at 15lb 2oz. Hope this helps.