1991 Chevy S-10 Don't know what to do next.

Engine Performance problem
1991 Chevy S-10 4 cyl Two Wheel Drive Manual 100K+ miles

We are trying to avoid sending this to a shop. The truck pops and sputters. It makes a loud pop, sometimes a series of pops. It pops pretty violently at times enough to make the shifter jump around. There is smell afterward. It's my BFs truck. He said it sounds like its popping back thru the intake. We've had the distributor replaced when we got the truck, as well as cap and router. He's checked the timing on it several times. New EGR valve. The compression isn't high enough, less than 100 in all cylinders The timing gears have been checked. I'm not sure if its related but the truck cranks several times before it starts up. We are out of ideas and trying to avoid paying labor costs at a shop.

edit: we've also changed plugs and wires. And it leaks around the valve cover? Could this be the cause of all the trouble?