Hot Courage 20 acts like it's running out of gas for a few seconds, but doesn't. Fuel tank venting?

[cmayo]

First major mowing (1.5 - 2 hrs) after spring maintenance (spark plug, oil & filter change, air cleaner & pre-cleaner), after an hour or so, engine started sputtering like it was running out of gas. After a few seconds, engine smoothed back out. Pattern repeated every few minuntes for the remainder of the job (45 minutes or so).

First thing Google turned up was improper venting/bad gas cap/vapor lock, so that's where I'm starting, but I don't know how the fuel tank is vented or what a good system is supposed to feel like. I'm assuming that the hose running between the air intake (point 1 on the attached photo) and the gas tank (point 2) is providing ventilation for the tank to keep the fuel flowing.

If I pull the hose at points 1 & 2 and try to blow through it, it feels about right for a 3/16 inner diameter hose so I don't think the hose is blocked.

If I pull the hose at the air intake (point 1) and try to blow through it with it attached at the tank (point 2), the hose seems almost completely blocked. I don't know how much air is supposed to be getting through the fitting on top of the tank, but my lungs weren't able to push any air at all through it that I could tell.

Pulling the hose at point 2 with it attached at point 1 (at the air intake), I can get air through the hose and the fitting at the intake. Not as much as through the unconnected hose but probably plenty enough to vent the tank.

So... if I'm supposed to have clear airflow into the tank at point 2, then that fitting on top of the tank must be clogged. I can't find anything on YouTube (or elsewhere) that describes the fitting or how to remove and clean it, and I don't want to hit it with the compressor until I know more about it and can get if off the tank.

Any thoughts on whether I'm on the right track and/or how to get the fitting off the tank at point 2?

 

[cmayo]

Update. Did some more digging and for anyone's information, the "fitting" at the top of the fuel tank is a
Troy Bilt Part 751-12118 Rollover Valve. It's a vent with a little floating baffle in it that closes the vent and prevents fuel spillage should the mower roll over. I took one off a 2009 parts machine I have (attachment) and Troy Bilt's apparently still using the same part # on my 2014 Horse XP.

I should be able to confirm or eliminate venting as the problem next time I mow by loosening the gas cap so the tank can breathe next time the issue occurs, and will try to update this post then.

 

[bertsmobile1]

Next time it happens take off the fuel feed to the carb and blow back through the fuel line.
Could be debris accumulating in the fuel line blocking the flow so the float can not completely fill .
Being a gravity tank it does not take much to impeede the flow.
If you left the mower all winter full of fuel then you could have a clogged carburetor or a clogged cut off solenoid so you might need to remove the carb and clean it properly .
Best time to do your matainance is immediately after the last mow then drain the tank and run the engine dry .
Tip the left over fuel into your car / trucks / snow blower whatever and start with nice fresh fuel next season.

 

[cmayo]

Good point about fuel storage. We don't get much winter weather here in central Texas and there's usually some kind of work for the mower year-round, but this is the first winter I let the mower sit with fuel in it for any length of time. I plan to drain the fuel tank and try some fresh fuel (this spring was also the first time I tried adding fuel stabilizer to my gasoline). Once the tank's empty, I'll try blowing out the fuel line.

It picked up a new behavior today where it's running a little rough and surging a little after getting hot. This guy (https://www.lawnmowerfixed.com/mower-engine-surging/) says that if adding a little bit of choke makes the engine stop surging (it does), the issue is likely fuel starvation caused by a dirty jet in the carb.

Loosening the gas cap to vent the fuel tank didn't make any difference at all.

 

[bertsmobile1]

Yes
At the beginning of the season it is more likely to be corrosion or varnish build up on the carb solenoid or varnish build up on the main jet.
Does not take much of a restriction to make the new EPA approved lean burn engines to play up .
And both problems can still be a plug forming in the fuel tank outlet.

All of them will yeild the same result .

 

[cmayo]

What's strange, though, is that I'd already cut my 1.5 acre lot twice this season without any of these issues, and the problem started right after I did maintenance (spark plug, oil & filter change, air cleaner & pre-cleaner) and, for the first time, added a fuel stabilizer to my gas (Ethanol Shield, 2oz added to 5gal fresh gas). The very next time I cut the back yard (1.5-2hr job) is when the issues started about an hour into the run, so I have to wonder if something happened during maintenance that started the problem.

I found this blurb on a Sta-Bil myth-busting blog:

"If your equipment’s fuel system is already dirty and you’ve never used a fuel system cleaner (this is true for me), it’s possible the cleaning agents in a STA-BIL product will wash the dirt and grime off walls and into the fuel system. This is a common issue with older equipment and can end up clogging the carburetor.​

​

If you’re facing this problem, we recommend running a high-quality fuel system cleaner through at least one tank of fuel before you store your vehicle equipment."​

I used Ethanol Shield, not Sta-Bil, but maybe that's what happened here? They recommend a "high-quality fuel system cleaner" but don't name one. Anyone have any recommendations for a "high-quality fuel system cleaner" and, if the Ethanol Sheild knocked "dirt and grime off walls and into the fuel system," will a fuel system cleaner dissolve that crud?