What's wrong with petrol strimmer ?

This is a classic case of the carburetor membrane going hard and not allowing the crankcase vacuum to draw fuel to the carburetor. Buy from your lawnmower repair shop a carburetor kit. You will have to take the carburetor in with you as he has to find the number off the carburetor to sell you the correct kit. The cost is about $8.

i would try this if it applies before i adjusted anything. does it have a 3 stage choke. if it does, sometimes you pull to start with it on level 1 about 5 times, then move it to stage 2 and it will usually start. then you have to move it to stage 3 for trimming. sometimes you have to leave them on #2 for a bit and apply the throttle slightly to "warm it up".

sometimes if you immediately move it to the last stage (i mean the choke) the engine will cut out just as you're saying.

and of course, if yours doesnt have these "settings" then you're bound to at least have a choke. hope it made sense, i'm still have asleep.

good luck, someone can point you in the right direction

If there's a high and low mixture jets then screw the low one out about a quarter of a turn. If this causes the engine to stop then speed up the idle speed screw

check the fuel filter in the tank to make sure it is not clogged up as it seems like a fuel starvation