I need to know the spark plug gap.

Al, .025" is the plug gap for your trimmer,page 20 in your manual. There may be a recall on your model to do with safety.
Check the attached links,instruction and guides, Good luck
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http://lawnandgarden.manualsonline.com/manuals/mfg/troybilt/tb475ss.html
Troy Bilt Model TB425CS Parts
Troy Bilt String Trimmer Sold at Lowe Recalled for Laceration Hazard

Remove the plug wire boot from the plug and the use a 16 mm. socket to remove the plug. Check the gap on the new plug and install in reverse order.

Standard plug gap is 0.5mm

the bolt on the end has left hand threads not right hand the most bolts have

Hello, Johnny -

The correct gap is .020" (0.5mm).

Link to specification page in owner's manual attached.
Troy Bilt TB20CS Operator Manual Specifications

change spark plug and check the gap between points

Check and clean your spark arrestor located behind a diverter plate on outside of muffler. You'll need a #25 Torx, or one slot screwdriver and wrench to take the plate off. Clean it with carb cleaner and wire brush and re-install. If this screen gets clogged, it could lead to fuel spray coming out of carb throat. Clean and re-oil the sponge filter while you're at it. Hope it helps!

http://www.m-and-d.com/pdfs/MTD/TB25CS-41BDT25C063PL.pdf

Probably the recoil spring is broken.

Since the air from the air filter does not go through the carb, the carb cleaner will not either. If you remove the carb and spry all of it that you can get to, you may get the plug. If you were to open the carb and go through it and clean it you would need to get new gaskets and maybe that will do the job. You may be able to adjust the carb. There is a "hi" and "low" setting. Try adjusting the "hi"...Lee