It sounds like the previous owner had the same experience and continued backing out the needles in the assumption that they were initially set overly lean.

If you have the model with the remote needle valve assembly, you should check the line from the needle to the carburetor for air bubbles. You should also consider taking the fuel tank and fuel lines out and inspecting the whole system. Many "engine problems" turn out to be tank or plumbing issues such as problems with the clunk line or a vent tube flush against the top of the fuel tank.

If the fuel setup looks OK and you're still stumped, find a flying buddy who is good with engines to help you go through the thing. Remove the carburetor and mount it again assuring pressure on the o-ring to prevent air leaks. Go around the cylinder head and back plate looking for loose bolts. Take a clean piece of fuel tubing and blow through the needle valve assembly to assure that nothing is blocking the flow of fuel into the carburetor and that the needles are passing air (and therefore fuel) when you blow into the tube.

The good news is that the GMS .47 is a terrific sport engine that is very powerful and transitions super fast when set up and tuned properly. If you work to get everything checked out and operating properly, you'll be rewarded with a powerful, reliable engine.

Good luck!