The MTD 46 SPO that has defeated me.

so, after a carb rebuild thrice, fuel line replacement, flywheel key replacement (it was sheared slightly, about 10mm off), new plug thrice, valve clearance check twice, governed spring checks, and leak checks, I still can&get this thing running/ idling correctly. I tried a new main jet, just in case it was the wrong one in. Any ideas, please do comment below. It&going to cost me £165 otherwise! ?