Small Engines (Lawn Mowers, etc.): wont stay running now no gas getting through, screw type, push mower

Question
Hello, I have a murray 3.8 22" push mower 10 years old. It would run for a few seconds and run when pushing the bulb. i took it to a guy and he said it was fixed but when i took it home it did the same thing, i know nothing about lawn mowers so cleaned the gas cap and then it ran for abot 20 minutes and wouldnt start again, so i started taking apart everything i could on it and when i got to this round cup like thing located below the primer bulb the gasket or rubber ring was pretty stretched out and cracked and a pointy ended square shaped unthreaded screw type thing with a rectangle spring on it fell out, i put it back how i assumed it went, the screw i removed to remove this cup had some holes in it, now, after that i couldnt get the gasket and cup to go back on very good and didnt know if the hole in the screw had to go any specific direction, but i put it back and now it wont turn over, i took it off and put it back several times and even cut and glued the gasket together hoping it would help because it was so stretched out, it didnt, and i wasnt sure where to spray starting fluid and one place i tried was under the air filter in this open line and when i did it started to try and turn over, i am sure now i am not getting gas beyond the thing i took off, gas came out when i took it off the first time and never again. i figured out how to drain the gas but wanted to change the oil, it is gray and sludgey, it has never been changed, but i couldnt figure out how, so please if you can help me, never worked on anything with an engine but i am good at figuring out things and if i knew what to do i am sure i could fix it with your help. the guy that was suppose to have fixed it is someone i wouldnt like to take it back to and i cant afford to get a new one nor afford to have it fixed by anyone else and my lawn is getting embarrisingly tall and now has a patch of mowed grass. also, could i pour gas straight in that line under the air filter and see if it would start too, i was scared to. please help and thanks again so much... ps. the mower has never stopped working before this.

Answer
Hi Jennifer,

Before you change the oil it would probably be best to get the engine running first.  

Try to start it while squirting fuel or starting fluid into the carb intake, under the air filter, where air enters the engine.  If it starts and you can keep it running by adding fuel, then the carb most likely has dirt, debris or gummed fuel inside.
You will need to remove the carb, disassemble it, clean all the small internal openings and blow it out with compressed air.   Probe each and every hole with a small wire.   A carb rebuild kit wouldn't hurt either, especially with the float bowl gasket that you mentioned being stretched.  

The square thing is the float needle.  It is supposed to move with the float.  It is attached to the float with the rectangle clip.

Let me know how you make out.
Michael