Maybe I can save you some time and frustration.
30 years ago I had this engine (Magnum GP 40) and some friends also, and frankly, they're garbage.
We all had the same problems, get it running right on the ground, take off and dead stick.
Of coarse we wrecked a few planes doing this, not fun!
I believe they were defective, air leaks most likely, some of my friends returned them to the hobby shop.
I did get mine to run consistently on 30% nitro but at to great a cost.
I wouldn't use one again, to many other good reliable engines to be had.
That's my experience for what it's worth.
Scott