Lawn mower question

I have a 15-year-old Sears 4hp mower that I change the air filter, plug & oil each spring. It started & ran fine last week for the first mowing, but now it acts like it's running out of gas. Runs full fast then slows way down, back up again, etc. What could be causing this? TIA
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Nelly Wensdow wrote:

Hi, Fuel delivery problem? First I'd try with gas tank cap off.
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Yes, fuel system is the likely place to start. Dirt, gumming up of the carb, sticking float, etc are possibilities.
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On Sun, 3 May 2009 11:21:26 -0500, "Nelly Wensdow"

Does it have the carb with the round fuel bowl that is held on with a single bolt at the bottom? I had a sears with that carb that did exactly what you described and it turned out to be a bunch of water in the fuel bowl. Took the bowl off, emptied it and let some gas run out and put it back together. It ran fine and then started doing it again and I repeated the draining and it's been fine ever since. The first time I drained it you could see the water 'bubbles' in the gas in the fuel bowl.
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Ashton Crusher wrote:

Amen! You can dump what's in the bowl and see if the float turns the gas on and off. I'd also unscrew the jets to see if they were clean.
If there's no fuel shutoff, you may be able to clamp the gas line. If the bowl is held up by a screw in the middle, be careful of the gasket. Be careful of the gasket at the rim of the bowl, too.
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wrote:

but
And if the float is OK a couple other things to check--is the choke staying on? Sometimes the cable will become loose and slip a little, the choke will stay on, and it will run until it warms up. Also check the tension on the governer spring. They can also become loose (stretched) over the years. There should be just the slightest tension on the spring with the engine off (assuming it's the type that I'm guessing OP has).
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Could be the govenor is sticking if it happens within a few seconds, its probably air vane , check linkage to see if you can move it and free it up moving it back and forth.
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It would need to be pretty old to use an air vane governor/rev-limiter. Haven't seen one for years.
I suspect the problem will be fuel system related. If you do have it starting well and running some, I will guess the flywheel key is ok. I would pull the carb bowl, but you might just give it a healthy dose of injector cleaner and let it run. The new alcohol blend fuel is extremely hard on small engines.
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How do newer govenors work.
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A gear inside the crankcase.
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Actually, a gear driven centrifical governor (spinning weights) . If the governor linkage from the carb connects to a lever on the side of the crankcase, that is what you have. Most 2 stroke lawn boys used the same type, but under the flywheel.
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