Bought this new and have always run non ethanol gas in it. Ran perfect for last 4 years and now it surges all the time and has lost some of its power. Air filter is good, I checked the plugs and they are good. Today I replaced the fuel filter and checked the fuel lines and all seem fine. Friend suggested I put some seafoam in the gas and I did. Ran it for about 45 minutes and no improvement. The baffling issue is it seems to run fine going UP a hill but the power is still reduced. It has approximately 85 hours on it. Oil level is good. Moving the choke lever back and forth doesn't help it run any better.
Before I take it to the local dealer am open to suggestions.

Make sure the carb hasn’t vibrated loose
Pull on the “governor spring” and see if it’s loose. My LT133 was surging, I moved the spring one hole (to add more tension) and that took care of it.
Kohler or Briggs?? Do the valves need adjusting??

Its a B&S engine. I'd clean the carb first. bunch of how to videos on youtube.

Nothing runs like a Deere! LOL, I couldn’t resist.

Ethanol gas, not a good thing. Carburetor issues. Look at replacing it and its cost. same thing with a Honda mower. Ethanol gas ruined the carb. replaced it and all is well.

That. It's running lean for some reason.

Had one several years ago that had some 'bad' gas in it. Non-ethanol. Took damn near a tank of new to get it worked out. Still likely something in the carb/jets.

vacume leak maybe? See if you can choke it out with your hand over the carb. Last year I had an almost new weedeater , that wouldn't start. The year before , it ran perfect. Ran it out of fuel for the winter lay off, new fuel, but wouldn't start. Found that mud dobbers had plugged the exhaust tight! I will plug the exhaust next time when not in use.

First make sure the carb isn't loose, check/replace the fuel filter. if all that pans out take the carb of and clean it out good, that means take the jets out and clean them with wire.

The absolute best way to clean the carb is to drop in in a ultrasonic cleaner with water and a couple ounces on simple green.

I had a 300X, biggest $3000 POS I ever saw, after 3 years it lost power going up a hill, a year later they determined the trans was shot and out of warranty!

Dump a bottle of Seafoam in it.......

or buy one with a Kohler twin on it

Or

my neighbor girl works on Deere tractors.......

want me to send her over ?

Had a JD riding mower once. Biggest piece of crap I ever mowed with. Carb had issues from day one.

have one rusting away in the back yard.

I had the same symptoms with mine last year. I changed everything with no change. Then I changed the fuel line, from the tank to the carb, and it now runs great. It may be as simple a fix as mine was. There are several YouTube videos on JD's losing power and how to fix. Good Luck.

If it’s a Briggs with the Nikki carburetor, replace it with a Ruixing carburetor. The Nikki is a POS! Briggs updated to a Ruixing......a much better carb and a “bolt-on” swap!!! I fought ours for 3 years, before finding out about the Ruixing. It was near $100.00 Amazon).....but worth every penny! memtb

Removed the carb and cleaned it. No improvement. Fuel pumps are not to expensive ($10) so ordered one. If that doesn’t fix it off to the Deere dealer it goes

I fixed the same problem on a Troy-Bilt I am running now with a Briggs Intek by replacing the carb with a no name Chinese one I bought off Ebay. The name brand Briggs is probably Chinese too. I understand that some of the carbs on the new motors are hard to impossible to clean and figured it would be easier to just replace it. I'd check out what memtb said about upgrading the carb also if one is available for yours.

You probably already know this but you should be able to find a carb or whatever else by searching the net with the model number of your engine.

Finding a carb is not the issue. But spending $100 to chase parts without knowing exactly what is wrong can cost more than taking it to the shop.

Funny thing. That's exactly what I did with my L118 a couple months ago and it went from a dog to a swiss watch in no time at all.

Changing the line was an afterthought even, for some other basic maintenance I was doing on the thing!

Or both! Love that seafoam!

I just did everything you have done to my mower (19.5 HP B&S engine) that was surging and would only run with the choke on. I finally ordered a new carb and put it on and it is running like it is a new mower. Carb was about $20.00 from some Amazon dealer.

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No . her shoes are on the wrong feet.

Hubert. Dude. Really?