I'm oddly interested in this, too, as my 129 (with a 14hp transplant) occasionally chirps on start-up too. Hmm...:bigthink:

Must be little birdie then.

Backfiring thru muffler might mean your running rich and/or need a valve job especially on the exhaust valve.
Running it hard for a period of time gets the muffler really good and hot.
Along with too much unburnt fuel and kaboom.

Mine does it almost everytime I shutdown after mowing the yard.
Not even at full throttle, maybe 3/4ths to 7/8ths.

I hope yours is not backfiring out the carb.

Nope, not out of the carb. it's out of the muffler and has only been doing it since taking on snow duty last week. Didn't do it at all this summer. I think it backfired a few times engaging the PTO at WOT, and also at shutdown. Ive read a few threads on techniques to avoid shutdown backfire, seems bringing the throttle down to halfway for a minute or two before shutdown might help.

That's what I try to remember to do (throttle down slowly).
And it works most of the time if I remember.
If I don't, the wife reminds me for making her jump.

It's because the engine is hot and there's gas vapor in the muffler that explodes. Idle it down and let it run for a minute. It's not real good for the muffler.

Not sure if this "tinkled down" to CC engines, but on the full-size Farmalls, the torque/horsepower curves were optimized for the upper end of the RPM range.

As I sort of very vaguely kind of recall, the large tractors would be run up to full throttle (high idle) and then the dynamometer would load the engine till the tachometer would be on the rated PTO speed mark, and observe Horsepower reading on the dynamometer.

You never, ever start an engine and make it run WOT immediately, nor do you shut it off without letting it run at the lowest setting for a while. True on any engine you own. Let me put it to you this way.... How would you like it is I came into your bedroom, jerked you out of bed asleep, kicked you in the seat and made you start running as fast as you could. Then after running for hours, I just knock you down to the ground and tell you to go to sleep. You ever try to just stop running? Feels like you heart is going to explode. Well, no more than a human body likes these demands, the internals of an engine don't either. I can give the mechanics as to why, but there is really no need. Just know, it isn't good on it. Let your cub warm up.... and respectively, let it cool down. Your motor will last longer, won't backfire, and serve you way longer. :beerchug:

All engines produce power on a torque/hp curve. Tractors, cub cadet, most all diesel engines, along with stationary gas engines use a variable speed governor, and this type of "power setting" is true to them all. So, the answer is yes, it applies to the Cub Cadets too.

Jonathan:

Great explanation of torque/HP curves.

I know what I want to say.... I don't always make things clear when I try to explain. My intent was to say that I wasn't sure if the CC engines were optimized at the upper end of the RPM range.

I have to agree,leave the motor opened up and leave the PTO engaged. IF you need to throttle back when you back up but leave the PTO engaged. You will just wear the lead button on the PTO which is why it kept running. I have always found also starting in the middle and work your way to the outside has always worked for me. Keep the snow from blowing in your face because its cold...lol

Just takes seat time to get used to it. Good luck an hope you enjoy the years to come as I have enjoyed my time on the seat of my IH CC 104 with the CW-36. Was my grandpas an he gave it to me 20 years ago but I had to work it off by mowing his yard and cleaning his driveway in the winter. I gotta say it was well worth it because now I have a wonderful memory :)