They usually would say, I tested the compression gauge on my air compression and it reads same as the air tank gauge. I've seen quite a few chainsaws that would not start or run and reported as low compression due to guys testing with a automotive compression gauge or their testing gauge not designed for small CC engines or the gauge not reading accurate. I cannot find any info about a mityvac 5300 compression tester you mentioned. I've seen small saws run/start and cut good with 80psi and would normally be labeled as bad due to the compression and the saw just needed a fuel line or carb kit or other minor things. Then if a piston/cylinder looks ok and a saw starts and runs/cuts good I might not even use my compression tester.

(the saw was not going to run much longer due to the cylinder/piston being consumed)

I've seen saw engines have good high compression but the piston was severely damaged. Usually one of the first things I check on a chainsaw BEFORE I take a compression reading is remove the muffler and take a look at the cylinder/piston. They usually would say, I tested MY compression gauge on my air compression and it reads same as the air tank gauge. It can be used for both the 4 strokes and two stroke engines and lawn movers a one-time affordable diagnostic tool for all the motors in your household. It can be used with a wide range of gasoline motors. I've seen quite a few chainsaws that would not start or run and reported as low compression due to guys testing with a automotive compression gauge or their testing gauge not designed for small CC engines or the gauge not reading accurate and compression not the issue with the saw not starting or running correctly. This PMD compression tester might not be known as the best compressor tester for accuracy as much as for its versatility. I've seen instances where a guy would do a chainsaw rebuild due to their testing gauge not being accurate and when they got finished with their new overhaul their gauge would then read even lower.

If a small engine reads low compression I have a back-up compression tester to confirm such. To perform the test, crank the engine 4 times by turning the key in your cars ignition, then check the compression gauge for the result. I've built some homemade compression testers for small engines with good reliable results. (and schrader valves and their location for small engine compression gauges) It bogged down on some large branches and died once or twice, but otherwise it ran OK.You might review this thread about compression testing and testers. BTW the chipper seems to run fine, ran it for about 4 hours last week. Is there any other way to test the tester? Also is there any way to fix it? I sprayed some silicone lube into it but it didn't make any difference. Also the tester leaks down pretty quickly on both engines. I got about 50 psi one that but I think it should be way more. Compression testing is a crude form of leak-down testing which also includes effects due to compression ratio, valve timing. The only other small engine I have is a Stihl chainsaw. A leak-down tester is a measuring instrument used to determine the condition of internal combustion engines by introducing compressed air into the cylinder and measuring the rate at which it leaks out. Last time I used it was to adjust the pressure on my espresso machine about 10 years ago. OMT Compression Tester, 8PCS Engine Cylinder Pressure Gauge for Petrol Gas Engine, 0-300PSI Engine Compression Tester Automotive with Adapters for Cars Trucks Motorcycles Marines ATV UTV 4. I don't even remember how old the tester is, maybe 30 years or more. I got out my old Craftsman compression tester and I got only about 30 psi. As part of the process I thought I would check the compression. It ran when I got it but I decided to do little TLC like change the oil, new plug, run some Mechanic In A Bottle and Seafoam through the carb. One is homemade from info about such on this site and If one reads low I get a second opinion from the other. I bought a used wood chipper/shredder with a Tecumseh 8.5 hp engine. Very good: I have TWO small engine compression testers. Getting started Check Engine Tester Check Engine Tester - Manufacturers, Suppliers, Factory from China.

Homemade compression tester