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I personally view compression tests as only a "quick look" diagnostic tool. There isn't a lot of difference in price between a good compression tester and a good cylinder leak down tester. If I were going to have only one diagnostic tool for checking engine health it would be a cylinder leak down tester because it not only provides a percentage of leakage of the cylinder it also assists in finding where the problem lies, i.e. rings, leaking valves, head gasket, etc. The caveat is that you need an air compressor capable of working the tester. A compressor that puts out 5 CFM is probably sufficient in most cases. You don't need a lot of CFM is you don't have a large engine (big diesel for example) or large leaks. You will need the ability to hold 120 PSI.
The short story on the methods cylinder leak testers can be used to locate sources follows:
After applying air pressure to the cylinder in accordance with tester instructions you can listen at the air intake (carburetor/throttle body) and muffler outlet for sounds of escaping air. If found valves are leaking (clearance, carbon, burned seats). Remove oil fill cal and listen for high volume of leakage. Low volume is normal (all rings leak a little). Remove radiator cap and look for bubbles (head gasket). Apply soapy water around outside of engine at cylinder head,cylinder interface and look for bubbles (head gasket). Apply soapy water at any suspected areas of leakage on engine surfaces (checking for cracks).
If you choose to go with a compression tester remove both plugs, set throttle plate to wide open position carb or throttle body), choke off if carbureted. Tests are more accureate when engine is warm but that isn't a possibility if you can't get it running. Be sure battery is fully charged to get proper cranking speed.
 
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If the engine won't run and the plugs are dry you probably aren't getting fuel into the cylinders. Open the throttle place and shoot a little carb cleaner into the intake manifold and crank. If it fires off and dies fuel is at least part of the problem.
Wet plugs would indicate either no spark or flooding (too much fuel).
I believe you could remove the fuel rail and injectors and test out of the engine but I've not done that.
 
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Do you mean to remove the air intake tube that attaches to the throttle body, open the throttle and spray some carb cleaner in there then try to start it? Not sure if I'm understanding you correctly on carb cleaner into the intake manifold.
Yes, exactly. Spray carb spray directly into the throttle body with the throttle plate open and try to fire it up. If it pops off and dies it's a fuel problem.
What you are doing is providing fuel directly, bypassing the normal fuel system. The carb spray is the fuel.
 
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Low compression is at least part of the problem.
 

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The cylinder to cylinder variation in compression is pretty high.

Dirt in the air box past the filter is not a good sign for rings and may be the reason your compression was low. Low compression can also be caused by rings that are stuck, stuck in place and filled by carbon due to poor maintenance, incorrect fuel mixture, lots of low speed lugging/idling, incorrect oil use or any combination of the above. Sometimes stuck rings can be freed by using "magic elixirs" which are poured into the cylinder or intake. Success is low. You might want to recheck your compression cold and if it's low see if adding about a teaspoon of motor oil to the cylinder through the spark plug hole increases it dramatically. If so the rings are stuck or shot.

I don't know much about your air box but I do know that the air box on my 2015 Ranger 570 FS has to be carefully installed to get it right. Throwing it in place and clipping it without close attention to fitment will almost certainly allow dirt to enter the engine.
 
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