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

[FatJack]

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).

UPDATE: Hi All, thank you for all of the input. Yesterday I swapped out the paper filter for one of those red plastic filters (yes, the same one that Steve's video says is worthless) and now the engine runs great right down to empty. I also made a slight change in the fuel line path by bypassing the little plastic harness that hangs off the bottom of the fuel tank. That harness keeps the fuel line from flopping around but also makes the first few inches totally flat instead of a nice downhill feed down to the carb. I believe the original filter was the red plastic type and I changed it out for the "good" kind a few seasons ago because that is what Sear Parts Direct gave me as a compatible filter. I changed it out a 2nd time when this problem came up last year, so a dirty filter was not the issue. I suspect that the paper filter is just too fine unless you have a fuel pump to force the fuel through.

 

[FatJack]

The stens paper filter seems to work ok with gravity systems but i fit the red screen filters on customer machines just to be sure. Every year i get a couple mowers in where cust wanted a better filter and installed a paper one and then have fuel flow problems.

Yep! That was me, though I didn't ask for a better filter, it's just what Sear's sent me as the "compatible" filter. Now that I know a micron from Nikon, I know better.

 

[Born2Mow]

Don't pat yourself on the back too fast. You forgot to ask "Why?"

Why is the filter clogged ? I've owned a TroyBilt with a Honda engine for 17 years. The filter is not clogged on it.

What I'm saying is that the clogged filter is merely a Symptom of another problem. Unless you fix the real problem, then you need to be buying your filters by the case. And you can buy any color you want because they'll all be clogged again in short order.

 

[Hammermechanicman]

UPDATE: Hi All, thank you for all of the input. Yesterday I swapped out the paper filter for one of those red plastic filters (yes, the same one that Steve's video says is worthless) and now the engine runs great right down to empty. I also made a slight change in the fuel line path by bypassing the little plastic harness that hangs off the bottom of the fuel tank. That harness keeps the fuel line from flopping around but also makes the first few inches totally flat instead of a nice downhill feed down to the carb. I believe the original filter was the red plastic type and I changed it out for the "good" kind a few seasons ago because that is what Sear Parts Direct gave me as a compatible filter. I changed it out a 2nd time when this problem came up last year, so a dirty filter was not the issue. I suspect that the paper filter is just too fine unless you have a fuel pump to force the fuel through.

I like Steve's videos but he needs to sober up and study up on fuel filters and fluids.??‍

 

[Scrubcadet10]

I like Steve's videos but he needs to sober up and study up on fuel filters and fluids.??‍

"How well does a ice cold Beer flow through a red briggs filter, compared to a paper filter"

 

[Hammermechanicman]

"How well does a ice cold Beer flow through a red briggs filter, compared to a paper filter"

I need to do go get a couple more cases of beer. I'll get back to you tororrow.

 

[ILENGINE]

Used the Briggs 691035 style filters on all of the smaller Kohler, Briggs, Tecumseh powered riders for years without fuel flow issues. Started having issues with fuel not flowing properly out of fuel tanks in 2012 which is the year that they discontinued the vented fuel caps and started using the vapor recovery type systems which operate under a slight tank vacuum. So for the non fuel pump riders I use the white pancake type Briggs filter. I will not use the red pancake style filter on any engine Long story for another time but had issues in early 2000's with sand infiltration through the red pancake filters causing the float valve not to seal.

 

[bertsmobile1]

It smells funny to me as well.
The pressure head should be more than enough to allow the fuel to flow.
I was thinking about water contamination blocking the filter but usually only happens with the felt filters

 

[Hammermechanicman]

There is nothing fishy about it. Some tanks are literally even with the top of the carb the pressure head is almost zero. All fluids have some sort of surface tension. Gasoline is very low compared to water

From the petroleum institute of America

"The surface tension of water is approximately 72.3(10 -3 ) N/ml, whereas the surface tension of gasoline is 21.60 (10 -3 ) N/ml [24] .Dec 24, 2020"

When the pore size of the filter element is small enough at a certain point the fuel will stop flowing. Usually around 1/2 full. What also happens is the fuel stops from fuel starvation and they pull off the fuel line which breaks the surface tension and then capillary action starts and fuel flows freely then they put the fuel line back on and after the float bowl fills the flow rate drops to zero again and surface tension stops flow through the filter and engine dies in a few minutes. most riders have the tank a little higher so you can usually but not always use a paper filer on a gravity fed rider. I have had mowers come in the shop that have been to dealerships with real mechanics and not a hack like me with surging and fuel delivery problems from the wrong filter. They usually have new carbs and coils and fuel lines too.

 

[Born2Mow]

...but usually only happens with the felt filters

Two ways we can answer this....

• That's exactly the way I felt.
• Stop groping those filters before installation.