I bought a Stihl 011AV at a garage sale for $5. It is in great shape, but the carburetor was disassembled. I put it back together, repaired a loose contact to the spark plug and now have good spark. But it will not start, not even a pop, even with fresh gas (or starting fluid) into the carb. I checked the compression with a Sun automotive compression tester(with valve in the tip) and I get max 50 lbs after 10 seconds of pulling. I took the muffler off and the cylinder walls look good. Any other reason I get such low compression?