My mom has Husq 125BT backpack leaf blower, the blower runs ok once it gets started but after about 15 minutes it shuts off and is extremely hot, what causes that and what do i need to do to fix it?

it might be the coil my chain saw did that put new coil on and that fix it.// had another chain saw do that it was full of dirt cleaned it out and that fixed it.

Hair dryer on carb.

sounds like it needs a carb kit can get and fix or take to a small engine shop

Most small engine shops and big box stores like home depot sell generic replacement starter rope. If you want the exact part from Husqvarna, there are 2 engine variations for the 125BT. The rope for the AC57 enigne is part# 531009567, the rope for the AC55 engine is part#531009653.

sears parts and service with model #

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Try pulling the muffler off and checking for blockage in the exhaust port, expecially the small hole above the main exhaust port. This is the same thing that my 125bt was doing this season and after cleaning out the carb with no improvement, I found some carbon build up in the exhaust port. The small hole above the port was completely blocked. After cleaning up all of the carbon buildup, it ran back to full power again.

GAP is the opening between terminals at the end of the spark plug ( on the threaded side of the spark plug) but spark plugs should come with the right gap from factory, as for your problem with to restart your blower it is ok just need to let cool down for 15 min or more.

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if you've ran it for any length of time you will need a new cylinder and piston/rings and cylinder gasket ,
take the muffler off and look for scoring /scorching on the piston

You could unplug the the wire on coil and chek again for spark, Good luck.

Remove the muffler and inspect the piston, rings and cylinder for vertical scoring. If so You may need a top end rebuild.