Lawn tractor engine problem

Last year I bought a Murray lawn tractor with a 21hp B&S I/C engine. Aside from the pulley housing on one of the blades disintegrating, it's been ok, not great (Murray reimbursed me for the repairs, but said that this was a "one-time" thing, not to expect them to honor the warranty every time - I'm serious!). Anyway, I've used the mower about 8-10 times to mow about 2+ acres over the past year, and last week just as I was finishing, the engine started surging and just before it quit, I pulled out the choke a bit and it started back up. I mowed for another 15 minutes and eventually had to pull the choke all the way out in order to keep the engine running. The mower doesn't run very fast in this mode, and doesn't have a lot of power. Any ideas what could be causing the problem? Checked the air filter and it's clean, as is the fuel filter - Thanks for any advice
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Sounds like either bad gas, or dirty carburetor.
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To tell the truth, I hadn't thought about bad gas, but that is a possibility - or the gas could be dirty - I'll work on that this week and see what happens - thanks!
wrote:

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Don't forget to check your air filter.

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