Won't start, occasional backfiring through exhaust, new stock muffler. Checked carb, looks clean. Took side cover off, alligned the TDC marks about 1/8 play.

Any Ideas?

 

Yes. Might be a weak magneto. May need a new coil in there. Maybe something like this: http://www.cheapcycleparts.com...lighting-stators-.aspx

I bought one and it made starting a LOT easier! I tried 2 carbs and months worth of tinkering before finally replacing the magneto. Now it starts 2 kicks at most.

You could try cleaning the carb too. The pilot jet is might be plugged, making it run a bit lean (that's why its backfiring). You might not have the right air filter or have it sealed up good enough. When you modify air filters, you have to rejet. Put the airbox lid back on too.

Try cleaning the carb really well (blow compressed air thru the jets - or use the little straw on a can of brake cleaner) and put the air filter back as close to stock as you can get it. If it still won't start, have somebody pull you around the yard and see if it starts. If it does, then see if it will idle. If it idles ok and runs good, but you still have a hard time starting it.... You will need the new coil for the magneto 100% sure.