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A Troybilt walk behind mower with B&S 120L engine. I use 89 octane Ethanol FREE gasoline plus Stable at the recommended mix ratio.
Emptied the fuel tank of gasoline and refilled, just in case there is water in the gas. .
I have replaced the air filter, cleaned the prefilter, replaced the spark plug, replaced the fuel tank cap, sprayed some carb cleaner into the carb. I have put some SeaFaom in the fuel tank.
When I start the engine it often dies or trys to die, and while mowing it will often act like there is no gas. I always start with a full tank of fuel. It is anoying to be mowing andn have the engine just slow stop (as if out of fuel). I just pull the starter rope once or twice and it will start right back up.
I can not remember it I rebuilt this carb 8-9 years ago or not. I have ordered a replacement carb (today) to see if it is the carb. I am running out of options as to what to check.
Any good ideas?

Two things come to mind outside of carb issues. One the tank may not be venting properly causing a vacuum inside the tank, and two, something obstructing the fuel line causing slow fuel flow from the tank to the carb.

Thanks ILENGINE. The fuel tank vents through the fuel cap, that is why I replaced it. That was one of my first thoughts was some vacuum in the fuel tank.I will check the fuel line for any obstructions. I still have thoughts of some debris floating in the carb bowl and it moves around and maybe blocks the main jet. I will drain the carb bowl and check the main jet for any debris that could cause this type of problem. (even though I have a new carb on order).

Your signature indicates lots of small engine experience, I appreciate your help. I have BackYardMechanic (BYM) experience in lawn mower engines, up to 13hp, chainsaw engines, various Sthil engines, and some automotive engine work (Dodge 225ci, 3.6-L pentastar (2), 2.8-L dodge V-6, Izusu I-4, Mitubitshi I-4, & 3.0-L V-6 . I still use a torque wrench when required And I am still learning.

First thing I usually check is the float bowl. More often than not it will condense water
into the bowl and will cause the engine to sputter and die. Drain the float bowl and
could be water or something obstructing the pick up of fuel. Whatever it is sounds like
fuel starvation. And Welcome to the LMF!

You might be spot on. It does act as if there is water in the gas. that is why I empted the tank and refilled with fresh gas, but still had the same problem. I will look at the bowl, float, and that area for water, foreign material, and see if I can get it going smooth again. Another reason why I use Ethanol-Free gasoline, to keep the water out of my gas.

Those engines with a float bowl will condense water over time no matter the fuel type,
stored inside or outside garage or shed or under a tarp. It's so very common I always
check that first. Don't see those old Chrysler 225's anymore. I had one in my new 72
Dodge 2 Dr. Dart. Navy blue, 3 on the floor. Wow I miss that old car. On flat ground
she'd peg the speedometer at 120 MPH.

DaveTN said:

Those engines with a float bowl will condense water over time no matter the fuel type,
stored inside or outside garage or shed or under a tarp. It's so very common I always
check that first. Don't see those old Chrysler 225's anymore. I had one in my new 72
Dodge 2 Dr. Dart. Navy blue, 3 on the floor. Wow I miss that old car. On flat ground
she'd peg the speedometer at 120 MPH.

Click to expand...

Mine was a '73 Dodge Dart Sport, Baby Blue, had it for 13 years, replaced water pump, oil, coolant, and the gaskets on the spark plug tubes, and the valve cover gasket, and last brake shoes (4 x Drum Brakes) Great car and my wife and I loved it, and hated to sell it.

I checked the main jet and float bowl, and I found a bunch of gunk on the main jet. I cleaned the bowl, and main jet with carb cleaner, applied carb cleaner to the carb, held the throttle vane open so I could spray down the venturi of the carb. Put it all back together, cranked it. With all that carb cleaner, it took about 8-10 pulls before it started. The engine ran like it should with no slow down or stopping. To dry her to mow yet, so I will have to wait to see how it does after running 15-30 minutes, but I feel like I got the problem cleaned up.
Thanks to all for the suggestions.