I am either missing, not understanding, or just plain don't know something here. I have three different engines on three different planes that will not accelerate past half throttle.

O.S. 40 FP with 10x7 in raider 2
Tower Hobbies Pro 46 with 10x7 in another raider 2
Magnum 61XL with 11x8 in P-51 Mustang 60"

They all seem to be running good (best as I have been tought or learned), slightly rich with pinch test and light smoke trail. All running recommended recomended props, (or as close to as I can get right now) and 15% fuel. All throttle linkages set correctly and have free operation. Best I can figure is load / RPM (incorrect Prop??) issue, but I don't know because diffent props don't seem to help. Could someone please enlighten me as to what I am missing here and put me on the right track to resolving the problem. Or if the only problem is me.