1. dirty fuel filter
2. dirty air filter
3. wrong mixture of fuel.
4. ignition coil gone bad.
5. old gasoline.
6. split in priming plunger bulb.
7. cracked fuel lines, either in fuel tank, or outside of it.
8. kids messed with it while you were at work.
9. All of the above!
Need to know how to replace the fuel lines into the tank?
Take sample of hose to lawn mower repair shop-not HD or Lowes-they don't know much, and can do less! Also take the name and model of the machine, and any numbers on the ident tag! Buy 2 feet of hose.
After you get the new hose, you'll try to stuff it into that teeny hole in the fuel tank, and it will not go in! Using a sharp razor blade (Single edge) taper the new hose about 3 inches back from the cut end, then lube it well, and work it into the tank. Put enough in there so it will pick up fuel at any angle! Using a wire hook, fish out the inner end, trim off the taper and install the new fuel filter, then stuff it back into the tank, and then put the other end onto the carburetor. If the carb has 2 hoses, replace both.
If there is no spark, then a new ignition part(coil) is probably in order. This is where you have to balance the cost of a new ignition, against the cost of a new machine, which sometimes is the best route to take! Of course, before taking that step, inspect the machine to make sure there isn't a loose wire or connection. I've picked up a number of trimmers that were tossed out by owners, and which had some of the symptons as set out above. Not all were made to run, and got the deep six!
HTH: Rustyj

If you haven't replaced the spark plug in the last year or so, I would do that (or, at least clean up the current one). Also, if you haven't cleaned the spark arrestor screen lately, do that, too. Both could have an effect on how easily your trimmer starts...and runs.
js

where should the second fuel hose be connected?