Juan,
I had Byron Barker rework an RC ST 45 which is one of the new Chinese made engines. He hemied the head, did a little minor re-timing work and made the venturi with a sprinkler ST needle valve.
Engine runs a very consistent 2-4 break. he has reworked several of my engines and this one is by far the best. Look in the magazines for CF Slaterly Company, he does a great job and is a heck of a nice guy.
Tim