The mouthpiece just didn't "feel right" when playing the horn.

Yamaha’s are known for being great mouthpieces with phenomenal range, but at the same time having the capacity to reach low notes ringing in the low register.

I also purchased a gold 5g mouthpiece seperately and it has improved my experience with this euphonium even further.

I suspect that my perceived intonation issues would improve with a better mouthpiece.

The only thing I didn't like was the C comes out very flat