'71 w/4Cyl. Engine Problmes...

I have a guy's Jeep here,
4 cylinder engine (plastic valve cover leaking!)

He's been to 4 shops, had the head done, reground valves, no head gasket leak, (I used leak detector on radiator),
But he's getting a ton of blow by, full of 'Rotten Milkshake',
Compression is good on all cylinders.

It's also got some sort of fuel problem, goes about 20 minutes or so, loses power and won't run.

I'm thinking carb rebuild, but the blow by issue is what is getting me stumped...

Any ideas where to start looking?
Anyone had this problem and figured out what it was?