921UL oil burp

It should burp just fine especially at warm temp.  50 blades is excessive.... but could be.  Do you turn prop slowly?  The burp sound is from piston / cylinder blow-by that makes the crankcase pressurized and that is what causes oil to return to the holding tank.  You hear a burp when the last bit of oil is returned to the tank and then a slug of air follows up the return hose and causes the burp sound. 

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Each engine is slightly different. Some burp with just a few turns and some take 40 turns. If it doesn't burp right away that usually just means there's more oil in the bottom of the crankcase and it just takes more prop rotations to get it back to the oil tank. Things like oil tank height compared to the engine, older engine, older style oil filter, ect... can add to extra oil in the crankcase.

"50 blades is excessive.... but could be. "

Could be what? Since this was the third time I had not heard the burp, I thought I would turn it until I got it to burp as it always had since June 2022. Because I have been chasing ignition and carb issues since June and have run the engine in relatively short intervals many dozens of times, I have "burped" it many times, but the last three or four times there has been no sound. Only one time (without the sound) did I turn it extra slowly. I'll try that again tomorrow.

You can run the engine and let the system return the oil and then check it.

This happened to me. After much head scrstching it was just the overflow tube twisted and thus blocked at the top of the tank. I hope thst is the cause!