I had this identical problem with my Toro lawn mower. It's about 10 years old. Always started first pull when hot or cold. Now it takes a couple of pulls when it's cold, and won't start at all when it's hot. I need to let it set 15 minutes after stopping it to empty the trimming bag. I tried a couple things suggested here. I replaced the spark plug and air filter (first time since buying it). I also tried loosening the fuel cap such that it wasn't air tight, to see if a vented fuel cap would solve the problem. None of these changes made any improvement in my hot starting. Then I started messing with the choke. I'm not a motor guy AT ALL. I added a picture that indicates where the choke is on my mower. I shoved a clothes pin into the choke to force it closed, and the mower started first pull. I had to pull out the clothes pin quickly so it would run smoothly. So I loosened the screw holding the choke, which I highlighted in my second picture, sprayed some WD40 at the connections, and cleaned the grass and dirt from it. Now it runs great and starts first pull hot or cold.
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