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So I have a John Deere X300 that I bought many years ago but almost never use. It has maybe 40 hours on it.

Decided to go out and get it running again so I changed oil, filters, put fresh gas, and new battery. Checked the plugs and they look great. No oil or fuel fouling at all.

The problem is that when I increase the throttle, the engine seems to have a miss or stumble. I can watch the lever "hunt" against the stop. However, I noticed if I hold the choke closed, the engine runs like an absolute CHAMP and is totally steady.

My old-school tuning brain says that if I close the choke and idle increases, that means it's running lean. Fuel filter fills right up so fuel flow looks good.

I was expecting there to be some sort of mixture adjustment but I can't find anything and what I've read says there is no mixture adjustment on this carb (??)

I'd really like to get this thing working again but I'm not sure what to do. I see lots of posts about hunting JD's but they always talk about a mixture adjustment.

Anyone solve this problem before?
 

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Pull the carb and clean it. Sounds like the jet has crust on/in it.
 

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The key phrase here is " I bought many years ago but almost never use". You put fresh fuel in it but probably never drained out the old fuel before storing it. As mentioned by the previous poster, chances are the carb is clogged or gummed up. A good cleaning of all the jets and orifices should get it running smoothly again.
 

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or you could just get a new one:

Looks like there is a SN break, 2006 and newer have a bigger engine which needs a different carb, so make sure you get the one that fits. I would start with simple carb/gas cleaner. I have had good luck with SeaFoam when I had this problem many years ago. I now use Stabil 360 Marine all year round and find it works great.
 

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You could try cheating with a little fuel system cleaner. I pulled out the generator that I store dry and it acted similar. it began that it would only run off spray and not it's own supply. Gave it one last shot and it would then run with choke. About 3-5 minutes of running with fresh fuel (including stabilizer and fuel injector cleaner) and she began to purr without any other work and no choke.

There's one real trick here that helped me with it though. I brought it into the garage and put it next to the toolbox, prepped to pull the carb when I gave it another try. You need t scare the machine into knowning it has two choices, to run well or run well.
 

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Before taking apart the carb, I would try running some Seafoam through it. If the carb has an easy to remove bowl, that would be my next step.
 
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