We've all cleaned out lots of these mower carbies but they can be difficult to clean after water and old fuel gets into them.
One thing that takes a few minutes when the carbs are really blocked up is to linish the main jet / emulsion tube on fuse wire while twisting and using WD40 ,when the wire clears a blockage it's still tight sometimes but after a while the jet / emulsion tube is polished back to original size also the idle and intermediate holes near the butterfly must be clear ,I usually would blow compressed air though all the tiny fuel paths / air bleeds etc.
I've never had to buy a new carby like this design ,I've had a few that were too corroded inside to use but had another second hand carby, a lot of the time after linishing the main jet/emulsion tube they run smooth on full revs then by using 98 fuel to cut the grass it will clean out the idle and intermediate side of the carby but sometimes I rev the motor out for a few seconds at a time by the governor arm and that's enough to remove a small blockage.
Just a thought when you cant remove the main jet ,I have heard of people cleaning carbs on a stove top in a pot of 50/50 water and vinegar and boiling the carby ,you would think this would clean and get the carby hot enough that the main jet would undo easily.Sometimes on engines when I can't undo a bolt because it feels like it will break I run the motor until hot and the bolt comes undone without a problem (works well for head bolts on Briggs etc). I guess it would help if you don't have an Ultrasonic cleaner or if your cleaner is only 60 degrees.
