I want the name of that mechanic - I want to be sure I never take anything to him.
If he checked everything, then you would know why it's not running. Making a motor run is like baking a cake. When you bake a cake; you take the ingredients (flour, water, yeast, baking soda, butter, etc) mix them properly, bake them at the right temp and you get a cake.
With a motor; you have to have compression, spark, spark at the right time, fuel and air in the right ratio and the motor will run.
Start by checking the compression (with a guage - don't just put your finger over the hole). Compression in the range of 120 to 180 is good. Less than 100 is bad. (30 psi will blow your finger off the hole) If the compression is good, then spark and at the right time. Connect a timing light and check the timing as described in the manual. If the spark is OK, then fuel and air. Now the technical part - finding the source of the problem - if the compression is low, it might be valves or cam timing - if it has spark but the timing is wrong, it could be a sheared flywheel key or a crankshaft problem - if all is right up to this point, then it might be fuel, air or exhaust. Usually with an exhaust problem the engine will start, but won't accelerate past a certain point and might decrease speed till it dies and you could hear a hissing sound coming from the muffler. Intake is kinda like exhaust - it's gotta get air and fuel. Usually it gets too much of one or the other.
If it was running and stalled and all seems normal - sometimes just a new spark plug will fix it.
