Hi everyone, new to the forum and excited to learn about these very unique engines.  I just acquired a Changfa 1115 with an ST-12 head from an estate sale.  Brought it home and surprisingly it fired right up.  Being unsure of the grade and age of oil that was in it I drained it after running for about a minute.  Replaced with straight 30 weight.  Engine starts right up and seems to run fine aside from a terribly disconcerting knocking sound.  I know these engines tend to be a little noisy but this sounds downright terrible.  Loudest when operating at the “start” rpm but definitely still sounds terrible at the 1800 rpm operating speed.  Anything I can do to confirm
If this is normal or not?