Totally agree, exhaust valve adj is critical. Decided to google briggs decompression valve. I know for a fact that honda uses the exhaust valve and cam for decompression. Wasn't sure that briggs did too. Here is what I found out.
There are two types, both on the camshaft. Lower HP (around 8HP or less) typically have a lobe with a bump on it that keeps a valve (often the exhaust) open at RPMS under 250, aiding in starting because the valve does not fully close)
Larger engines have a counterweight on the cam that swings "up" at the same RPMs are "removes" the high spot achieving the same affect as above.
The first time I was told to check the exhaust valve clearance on a hard to crank engine, I thought they were full of it. Come to find out, the small bump on the exhaust cam doesn't work if the exhaust valve isn't set to spec.