As you haven't included a picture of the install in the jet it's difficult to know but have you got full inlet ducting leading from the intakes to the front of the fan, and of course the shroud for over the fan and engine to enclose all of it? If you don't have full ducting from intake to exhaust you will have very little for thrust. That is why the byron fans were so inneficient. They were much larger diameter and required large cheater holes in the airplane. 1/8" rounded edge on the intake is very sharp, you are losing a lot of smooth air with that, 1/4" I believe is what was recommended. If the engine is running at proper RPM and your thrust is lacking then it is 99% likely a ducting issue, make sure your ducting is sealed and smooth from start to finish.