I was actually trained by carburetor and Briggs before going the Mercedes route.
I would start with fuel. 99% of all starting problems with small engines have to do with fuel (or lack there of). One quick way to check is to take off the air cleaner and put your hand over the air inlet and give it pull. IF it fires off, you have identified that you have a fuel problem and have to go into the carburetor and see where the restriction is.
If fuel is not the problem, check on the ignition system.
The only weird thing I have seen is a camshaft spun on the gear. You could not tell it was out of time until you set it beside the new one.
ASE CERTIFIED MASTER AUTO TECHNICIAN
MERCEDES SPECIALIST 11 YRS