Small Engines (Lawn Mowers, etc.): GAS TRIMMER wont start, zama carb, compression gauge

Question
Hello I have an older gas trimmer that ran perfect until last week. Now it won't start. I have spark when I removed spark plug and noticed my fuel filter was all brown and rusty..it had a screen type material on the oputside of the fuel filter that sorta desintegrated. I changed and put in new gas , tygon fuel lines and a new fuel filter. Also cleaned carb and muffler ..still won't start with fresh gas and oil..PLEASE help. I blew carb cleaner (with small red nozzle attached) into the holes in the ZAMA carb to clean it out... Someone said it ruins the valves inside carb if you use pressurized air to blow.
Is this true? Also, why isn't this starting..I have compression. THE MODEL is a HOMELITE ut20006 gas trimmer with a ZAMA carb c1U series..Thanks

Answer
Did you check the engine compression with a compression gauge?

If the fuel lines were bad odds are the carburetor diaphragms are bad as well.  Did you replace the carb diaphragms?

Is there a crankcase leak?  Look for signs of dirt or oil along parts that have gaskets.  Is the hole in the carburetor intake block open?  Is the crankcase pulse reaching the carburetor fuel pump?

I have not damaged any carbs with compressed air.  

Did you check out Zama's website for the carb maintenance manual?

Let me know.