UPDATE: SOLVED! Only runs if tank 1/2 full +?? Carb problem?

FatJack said:
Hi Gang, Hoping somebody might have run across this problem: My Craftsman tractor has a Briggs & Stratton "Platinum" 540 cc, 21 hp engine. It runs great with a full tank, but stalls out as the fuel level approaches 1/2. I thought it was a fuel line or filter issue, so replaced filters and replaced lines and didn't help. This problem is two seasons old now, just filling the tank is an ok work around, but thought I might try to fix it this summer.

I'm thinking it might be a dirty carb issue, but not sure why the 1/2 tank vs full tank would matter, unless a full tank supplies more pressure to push fuel through??? Not sure if that is even possible.

Before I spend the time take apart the mower to get to the carburetor, I was hoping someone could confirm that it is likely a carburetor problem. If it is, should I replace carb or just clean it? (10 years old tractor).

Thnx!
Click to expand...
I had a similar problem with my deere d140. It would starve for fuel after running for a while. I changed everything and that did not help. Carried to a national dealer, they changed carburetor ($500), did not help, and wanted to change manifold ($600). I told them to put my old carb back on, and I will pick it up.
I got it home and looked at everything I could , and did not find anything.
Finally I removed the gas tank, and Inside I find a PVC Pipe fitting, A brass Slug about the size of a quarter, and a brass ring like a key ring only bigger.
With the sleeve that is in the filler port of the tank, I was unable to get these items out of the tank, so I removed the intake from tank that feeds the engine. This intake is just a straight pipe with an open end that sits about 1/8" above the bottom of the tank.
The slug in the tank about the size of a quarter was getting suck up to the bottom of the intake pipe by the vacuum from the engine causing it to starve for fuel.
Solution: I cut 4 small "V" shapes in the bottom of the inlet pipe and and reinstalled it in the tank and reinstalled the tank in the mower, the foreign objects are still in the tank, but the engine has not stalled for lack of fuel since.
Not sure this is your problem, but it fixed mine. good luck
 
FatJack said:
Hi Gang, Hoping somebody might have run across this problem: My Craftsman tractor has a Briggs & Stratton "Platinum" 540 cc, 21 hp engine. It runs great with a full tank, but stalls out as the fuel level approaches 1/2. I thought it was a fuel line or filter issue, so replaced filters and replaced lines and didn't help. This problem is two seasons old now, just filling the tank is an ok work around, but thought I might try to fix it this summer.

I'm thinking it might be a dirty carb issue, but not sure why the 1/2 tank vs full tank would matter, unless a full tank supplies more pressure to push fuel through??? Not sure if that is even possible.

Before I spend the time take apart the mower to get to the carburetor, I was hoping someone could confirm that it is likely a carburetor problem. If it is, should I replace carb or just clean it? (10 years old tractor).

Thnx!
Click to expand...
I had the same problem with a kohler in my craftsman, the manual showed a 51 micron fuel filter which was for an engine with a fuel pump.
mine did not have a pump, after a lot of research, I found that it should be a 75 micron filter.
the only thing I did was put on a kohler 25-05021-s filter and have had no problem since.
might be something to look into.
 
Some suggestions....
  • I've had the same issue with clogged fuel strainers inside the bottom of the fuel tank
  • On a tiller recently, there was a bend in the fuel hose coming directly off the fuel tank. It was a tight 90 deg bend. Due to prolonged storage with fuel in the system, the ethanol ate up the inside of the hose and the bend collapsed. Fuel could only get through the blockage when the tank was full because of the "pressure" a full tank created.
  • Newer fuel tanks also have elaborate EPA-approved breather systems that only allow air to come in, but keep fumes from escaping the tank. These are usually EXTREMELY delicate flapper systems that newer fuels can make stick closed or make intermittent.
Not saying one of these is your exact issue, but rather the "full tank" requirement means it's far more likely related to the fuel cap, fuel tank, or the hoses and other bits that connect to the carb, rather than something inside the carb.
 
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Next time it happens remove the fuel line from the fuel pump. If fuel is flowing from the tank to the pump, problem is between the pump and carb. No fuel problem is between the tank and pump.
 
You definitely get more pressure to the pump when the tank is full. Seems like the pump has an issue.
 
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I had that problem with a John Deere for a couple years. I finally fixed it by taking the cap apart carefully and running a drill bit down through the center hole a tiny bit bigger than the original hole.
I had noticed the existing hole had a white scum ring around it from the alcohol in the gas. Reassembled the cap and it has run fine ever since.
 
Don't know which carb you have. Some had a screen behind the steel hose nipple. If it has a plastic nipple. I don't think it has a screen.
 
Sounds like your gas tank vent is clogged and your building up a vacuum in your tank. If there is a vent hole , you can clear it out with a small drill bit. Husqvarna tractor fuel tank caps are notorious for this.
 
Does the fuel line come out the top of the fuel tank? If so, it may have a leak about halfway down inside the tank.
 
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