Got a Walker zero turn mower last year, older one with a Briggs 400cc engine.

Machine ran great most of the summer, but started to stall out under load at the end of last season. Mow fine around the yard, but going uphill with the blades spinning or running into a particularly lush area of turf, it would want to quit. No obstructions in the fuel lines, including the new fuel filters. Gas tank cap breather is fine, not creating vacuum. Air filter has been replaced. That was as far as I got before cutting season ended. Any other knee jerk reactions to what may be the culprit before I just start replacing things?

BTW love the mower, especially being that it was/is made in US by a family owned business.

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On some nights I still believe that a car with the fuel gauge on empty can run about fifty more miles if you have the right music very loud on the radio. - HST

1983 300SD - 305000
1984 Toyota Landcruiser - 190000
1994 GMC Jimmy - 203000

https://media.giphy.com/media/X3nnss8PAj5aU/giphy.gif

Fuel quality in lawn equipment is an issue with ethanol blends. Extra moisture causes the water to precipitate out and adding "clean gas" doesn't fix it. Might be a factor. Check the fuel bowl?

Fuel quality is an issue.
Depending where you are in the country could make or break the ethanol problem.
Most hard start issues come from contaminated fuel from the homeowner. Any water in any gasoline causes corrosion in the pot metal/aluminum carb castings and any evidence of a powdery residue requires card replacement. You might get away with cleaning the carb w/powder but it keeps coming back.

Another issue is over mixing fuel stabilizer.

Located in eastern CT. Mower was shipped here to PO back in 83, and has spent it's whole life in about a 20 mile radius.
Hasn't had any stabilizer added. Tank was dry when I got it, and it has only seen about 4 tanks of straight RUG over the summer.

Seems like pulling the bowl and/or the entire carb might be the next step.

__________________
On some nights I still believe that a car with the fuel gauge on empty can run about fifty more miles if you have the right music very loud on the radio. - HST

1983 300SD - 305000
1984 Toyota Landcruiser - 190000
1994 GMC Jimmy - 203000

https://media.giphy.com/media/X3nnss8PAj5aU/giphy.gif

Are you sure it's the motor bogging down and not the blades? That your problem happens on hills suggests that it is not the blades, but my mower fooled me for a while when I thought the motor was bogging down when it was really a worn out mower deck belt that was causing the blades to slow down in deep grass.

Maybe wheel drive slipping? Old stretched belts do that, like Honus said.

I'm betting, due to age, that you have a gasket that has degraded behind the carb, allowing the vacuum to leak. This happened on an older B&S I have. Replaced the gasket and all is well.

__________________
1987 560SL
85,000 miles

Some times the intake man at the cyl cracks too.

True...

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1987 560SL
85,000 miles

I had a similar problem with a chipper/shredder. It was a governor issue, a spring wasn't doing exactly what it was supposed to do. Night and day difference.

Mostly I fight fuel issues with lawn equipment. A set of reams for cleaning welding tips has been helpful. Passages in carbs can seem clean but if they are not exactly round at the exactly the whole diameter they don't do their job and the engine starves for fuel. Hardened or leaking diaphragms or leaking fuel lines are the next round of issues.

Belts on riders are a huge issue. I have limited experience with riders but I dug into a couple at various times. I have sort of been wanting to buy one but I'll probably buy an antique yard tractor instead. I have had my eye on a farmall cub from the 40s or 50s.

I like old tractors, but if you want to mow grass, the modern high-speed mower decks are the only way to go.

One of my tractors is a 1959 Massey Ferguson 65. The gas engine it came with was not the best, so I got a diesel from a MF 165 and bolted it up. That tractor probably gets used 350 days a year. Works like a charm.

The deck is shaft drive. Only belt involved is a short one from the engine to the shaft assy. I pulled the shaft off of the deck and was able to turn the blades fairly easily by hand.

__________________
On some nights I still believe that a car with the fuel gauge on empty can run about fifty more miles if you have the right music very loud on the radio. - HST

1983 300SD - 305000
1984 Toyota Landcruiser - 190000
1994 GMC Jimmy - 203000

https://media.giphy.com/media/X3nnss8PAj5aU/giphy.gif

The drive wheels are powered by two independent hydrostatic transmissions which turn the axles by chain.

It will go up and down hills no problem, unless I have the deck engaged.

__________________
On some nights I still believe that a car with the fuel gauge on empty can run about fifty more miles if you have the right music very loud on the radio. - HST

1983 300SD - 305000
1984 Toyota Landcruiser - 190000
1994 GMC Jimmy - 203000

https://media.giphy.com/media/X3nnss8PAj5aU/giphy.gif

Seems like a carb removal is the likely next step, be an opportunity to check a number of things.


BTW the mower is a Walker M36-42. Never seen a mower built like this one, sorta like an older Mercedes, engineering was given free reign in design. In fact the prototype was built by the company owner and his son so they would have a good mower for their own yards.

__________________
On some nights I still believe that a car with the fuel gauge on empty can run about fifty more miles if you have the right music very loud on the radio. - HST

1983 300SD - 305000
1984 Toyota Landcruiser - 190000
1994 GMC Jimmy - 203000

https://media.giphy.com/media/X3nnss8PAj5aU/giphy.gif

Interesting......deck is sucking the power.....I'd seriously look at the deck rather than the carb.
I had a lot of returns for similar reasons and the past year was more rainy than others, one that reminds me of what you're saying ended up being dull blades and bumping up the idle speed. Most those engines should be running around 3000 rpm give or take....chk manufacturer specs.
You bend the metal tang that the spring from the carb hooks to usually to bump gov speed..
I'd try RPM chk and sharpen. Try the easiest and cheapest first.
When was last time the blades were sharpened?