My 125l started up , was running fine.Shut it off now won't start.

Did you changed fuel filter.

Take the gas filter off. Should be located near the front of the carbeurator, take off the air cleaner and look for it, it takes 2 wrenches to take it off, a little gas may spill out but not much and replace it, however there is a strong possibility that he gas pump is out if the filter is fine. Hope this helps

Does it crank?If you shut it off and you restart after a few minutes and it cranks but won't start or starts and runs rough the injectors are leaking and flooding the engine. Need better description

Have you put the gear head on correctly.? Are the ends of the shafts pushed in far enough?

does it get spark when it is warm, if not may be coil

sounds like the needle valve in the carbie leaking fuel past it,causing flooding

its not getting enough fuel. take the carb apart and clean it good. you can use a twist tie stripped off to clean the really fine holes or a wire brush wire. also you can burn the screen off in the carb. pull it out, burn off and use a drill bit or something similar to reinstall it.

You likely need to replace the muffler,this is a common problem and if the engine can't get rid of the exhaust it also will not take in more fuel,happens a lot with anything with a spark arrester in the muffler.

It has to be in kill switch replace it and see

Try this: The next time you run the trimmer, and it begins to die, loosen the gas cap. It should start running again. This means that the gas cap is clogged. Clean the holes out of gas cap, or buy a new one. (If this doesn't help, give a more detailed explanation the next time.)

Jim