I have an 28 cc McCullogh leaf blower which will

Your muffler may be clogged,may need a new one,take it off and see if it will start.

sounds like magneto going out .. it puts the spark to the plug

new spark plug is first option as when hot plug or cil pack will get hot and short out causing misfire will lead to none starter

At all? Check the plug to see if it's wet. If so you are getting fuel so problem is spark. Get a new plug and gap properly. What else have you tried?

if you have no spark check the kill switch and wires if there ok change the magneto

check the fuel lines for holes or cracks could be getting air

Try removing the muffler and look inside of the exaust port, you should be able to see the piston in the full opening of the port. If you can, try starting and running at wide open throttle. If it runs fine( a bit loud, so wear hering protection), then you have a plugged or partialy blocked muffler or spark arestor. Sometimes rich mixture can cause excessive carbon build up.

Hope this was helpfull.

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blown moter from bad gas mixture

i have aecho pb 260l backpack style leaf blower and it will not start. it turns over well and has spark and reasonably new fuel. any thoughts

If a small engine wont start its usually one of two problems, its not getting gas, or its not getting spark. easy way to find out if its getting a spark is to remove the plug, put it back back in the connector and just let it hang down while you try to start it. you should see a bright blue spark, if you dont try changing the spark plug. if its getting a spark come back on this site and i'll help you trouble shoot it.