Hmm... my US41 kinda felt and sounded the same- never really "got on plane" so to speak, ran great, reliable, but never screamed full throttle, just kinda "cruised" along about 6800 RPM with a Bennet muffler. Even the occasional "burble" full throttle- leaning it out caused it to dead stick. Only about 1 gallon through it too, maybe thats the problem, not broken in??