# Mystery mower fuel problem



## begreen (Jun 15, 2015)

Our 7 yr old 18hp Kohler powered Craftsman yard mower started having fuel issues this year. It's a simple gravity feed fuel system. The mower runs out of gas when the tank gets down to about 1/3 full if I am mowing uphill (even as small amount of incline). If I back up the same hill it will run fine. If I wait a few minutes then restart it will run again fine for sometimes as much as 10 minutes more. If I fill the tank it will run fine. The first thing I checked was to be sure the vent hole in the tank cap was clear. It is. The problem will even happen with the cap off. 

I have replaced everything from the tank to the engine block and the problem persists. When it stalls out of gas you can see that the fuel filter is almost empty. When the mower runs it runs great and cuts very well still. Power is good even uphill cutting heavy grass. Any thoughts on what's happening?


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## semipro (Jun 15, 2015)

Strainer or outlet in fuel tank clogged? 
I believe even gravity feed systems use a fuel pump on some larger motors. Maybe a bad diaphragm or clog there?


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## Jags (Jun 15, 2015)

Most of those tanks will have a water screen at the bottom.  Completely drain and dry the tank and see if that helps.  Compressed air from the hose barb side will help dislodge anything on the screen.


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## begreen (Jun 15, 2015)

No fuel pump. I don't see any screen in the tank, just a plastic nipple at the bottom. When I had it apart replacing the fuel line I did try using compressed air, no change. This is really baffling.


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## Jags (Jun 15, 2015)

Hmmm...no fuel pump on an 18 HP seems odd to me.  IF there is a screen it is a very fine mesh and sometimes very hard to see without a flashlight.  Not all have that.

Any heat shielding missing or removed causing vapor lock??  The cooling down thing has me kinda of baffled.  One of two things are happening there.  Either the "time" of cooling down is allowing for the fuel to refill the hose/carb/line or the actual cooling effect is causing something to happen.  Interdasting.


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## begreen (Jun 15, 2015)

Gas goes from tank right behind the engine, to fuel filter, to carb. Same setup as a model T. There has been no heat shielding removed. I bought the mower new and this is the first year I have done any engine service outside of regular oil and air filter changes. You can see that the fuel filter is not filling when it stops running.

I will take the gas tank out again and will closely examine for a micro screen. Maybe I missed this. Tis indeed wierd because for the first 2/3ds of the tank or about an hour it runs great.


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## Jags (Jun 15, 2015)

For what it is worth (not much) - I had a 12 hp that had a fuel pump go bad.  It is also now a simple gravity feed and it will not empty the tank before the engine will cut out from lack of fuel.  If you refuel right away, does it fire right back up and run for another hour?  If so - this tells me that the extra weight of the fuel is pushing enough past whatever restriction you have (that is why I was thinking about the water catching screen.)

Another test...when it dies, shake the crap out of the machine and see if it will run.  That is another way to get water to move.


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## semipro (Jun 15, 2015)

begreen said:


> Gas goes from tank right behind the engine, to fuel filter, to carb


I've seen the fuel pumps installed on the carb itself.  The intake manifold vacuum pulses at the carb move a diaphragm that pumps the fuel.


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## begreen (Jun 15, 2015)

Yes, if I refill the tank it will go on for another hour. That is how I had been running it last month.

No fuel pump on the simple Walbro carb that I know of, just a simple float system. Changing the old to the new carb made no difference in behavior.


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## Jags (Jun 15, 2015)

Another thought.  You said it still happens even with the cap off?  And that the filter will actually almost empty?  Does not compute.  That would insinuate a vacuum or a blockage.  When the filter is almost empty if you pull the line from the carb, will flow begin again?  You could use that method to isolate which side is the culprit.  Pull line from carb and if it runs fuel - carb side is causing it.  If it doesn't run fuel - line/tank side is causing it.


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## heat seeker (Jun 15, 2015)

Long shot - is something shifting and pinching the fuel line when you're headed uphill?


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## begreen (Jun 15, 2015)

No pinching or shifting, the fuel line is 1/4 heavy rubber hose. It runs through a chassis grommet to keep it neatly on it's path. The total run is only about 2ft.


Jags said:


> Another thought.  You said it still happens even with the cap off?  And that the filter will actually almost empty?  Does not compute.  That would insinuate a vacuum or a blockage.  When the filter is almost empty if you pull the line from the carb, will flow begin again?  You could use that method to isolate which side is the culprit.  Pull line from carb and if it runs fuel - carb side is causing it.  If it doesn't run fuel - line/tank side is causing it.


Can do. Though odd and frustrating if two carbs, old and new, have the same symptom.


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## blades (Jun 16, 2015)

fuel line should be replaced with the newer line designed for use with the ethanol fuel, not rubber line the fuel causes it to rot from the inside out. you have a fueline blockage, does the unit have a shut off valve at the tank?  could be blocked with some crud. Some of the metal tanks were lined with something to prevent rust but the dang lining breaks down in the presence of ethanol. Makes a gummy mess that can block any type of screen quick. also I hope that 1/4" fuel line was the id size and not the od as that would be pretty small line for a 18hp motor. Most units that size have a fuel shut off sol. if it loses power no fuel flow.


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## Highbeam (Jun 16, 2015)

I too have a 19.5 HP engine in my craftsman mower. No fuel pump, no fuel shutoff. Fuel tank also under hood right near engine. This is just like a motorcycle setup. Gravity feed to the carb where the float lets fuel in to keep the bowl full. Your problem is upstream of the fuel filter towards the tank. Something is preventing fuel from leaving the tank and making it to the filter. The open float valve in the carb is allowing the fuel to drain from the line and air to refill the fuel filter from below. A screen, a pinch, debris, etc. Your clear fuel filter is helpful in this diagnosis.

Start by disconnecting the fuel line upstream of the filter and try to let the tank drain into a gas can. I suspect the flow stops (or slows way down) before the tank empties. At that point, I would blow backwards through the fuel line and see if fuel begins to flow again. If not, then I would remove the fuel line from the tank. Does fuel pour out of the nipple on the tank bottom? If not then pull the tank and investigate what's plugging it. Then a nice drill bit would be running up through the outlet nipple and clearing that obstruction.


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## begreen (Jun 16, 2015)

I have drained the tank twice from the 1/3d full level and it drains fine, no stoppage. The old fuel line was fine, no blockage but just in case I replaced it all. The fuel line is all new. I'll try running a drill bit through the tank outlet when I do this riff all over again.


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## Highbeam (Jun 16, 2015)

So the fuel tank is free flowing to the fuel filter at all times but the fuel filter has no fuel in it. I know my craftsman OEM fuel filter was not clear. Could it be that your aftermarket fuel filter is designed for a system with a fuel pump? Regular automotive fuel pumps make 3-6 psi for the carburetor and could handle some restriction from a relatively tight filter. Your gravity system does not make 3 psi. It takes 83 inches of water column to make 3 psi and 12 inches only provides less than 0.5 psi.

Remove the fuel filter. Test.


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## begreen (Jun 16, 2015)

Good point, that thought crossed my mind too although I told the mower shop what the purpose of the filter was. The previous filter was the original and like yours opaque white and a bit larger cylinder. The mower had the same symptom with that filter. Also the gas seems to flow fine if I drain through the new filter. But I can order the Sears filter, it just wasn't in stock at the time.


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## Highbeam (Jun 16, 2015)

begreen said:


> Good point, that thought crossed my mind too although I told the mower shop what the purpose of the filter was. The previous filter was the original and like yours opaque white and a bit larger cylinder. The mower had the same symptom with that filter. Also the gas seems to flow fine if I drain through the new filter. But I can order the Sears filter, it just wasn't in stock at the time.



The absence of fuel at the filter, yet full flow from the tank to the filter is pointing to the filter as the restriction. Is it possible to eliminate the filter with a short section of tube or a longer fuel line?    

Carb float valves can get sticky too so when you have the fuel filter out I would recommend blasting down the fuel line to the carb with carb cleaner followed by a little air in case you have chunks of junk there. I know you swapped carbs but carb cleaner is like 96 cents per can.


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## coaly (Jun 16, 2015)

I'd put a short piece of tubing in place of the filter too, with very little fuel in it to see if it eliminates the problem. When all else fails, process of elimination. Very frustrating too.

When it dies, if you blow into the tank to pressurize it, and it fills the filter, that is a sign you're overcoming the resistance of the filter the same as more weight of more fuel pushes it through. I'd bet on the original filter getting slightly clogged causing the problem and the new one having more resistance causing the same problem when fuel is low............... I put the old glass bowl style on when there's enough room.

Some Model T's do that too; Henry Ford designed my 1921 Center Door Model T with the fuel tank under driver seat. On long steep hills, the tank becomes lower than the carb intentionally to run it out of fuel. No oil pump with splash feed allows the front bearing to dry out first on steep uphill grades. To protect the front bearing, it was designed to run out of fuel before oil ! You must turn around and BACK up steep hills to keep the tank higher than carb and oil to the front bearing.


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## begreen (Jun 16, 2015)

Um, and then what about the rear bearing?


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## coaly (Jun 16, 2015)

The oil is very deep in the rear and the flywheel splash provides plenty of oil there.







What would now be called the transmission was called the hogs head that holds the same engine oil in the rear.


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## Dr.Faustus (Jun 17, 2015)

put a bigger fuel tank on there, so even tho 1/3 if the fuel cant be used, you still have the same or better run time than you had before the problem.


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## begreen (Jun 17, 2015)

LOL That thought actually crossed my mind.


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## rustynut (Jun 17, 2015)

ok begreen, are you sure its a fuel problem ?......i had a situation with my ford lgt14d a while ago where it would stall out on the hill but only when going in 1 direction. Happened a bunch of times before i figured that one out. Turned out to be a broken motor mount on the lh side and when traveling the hill with the rh side of the tractor on the lower portion of the hill the lh side of the motor would actually raise up enough to lose the ground connection and stall out. Replaced the motor mount and been fine since....
rn


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## Tom123 (Jun 17, 2015)

Get any small engine tank. Garbage pick or whatever. I keep one around from a vertical shaft Briggs. Rig the tank and a fuel line right to the carb.  Isolate the existing tank and plumbing and see if there's a difference.


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## sportbikerider78 (Jun 18, 2015)

When this problem happens and the filter goes dry, what happens if you pull the filter off?  Is fuel freely flowing?  It would seem that it is not and that would point me towards your tank and/or fuel line.  
Have you pulled the line and drained the tank yet?

Lawn mower carbs are so easy to access, I'd pop the float bowl off and blow it out with compressed air, and then hit every little nook and hole with carb/choke cleaner.  

A good carb clean is easy insurance.


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## begreen (Jun 18, 2015)

The tank has been drained twice. Everything including fuel lines, filter and carb has been replaced. I have carb cleaner and will try it, even though this carb is brand new and has the exact same symptoms as the old one.


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## rustynut (Jun 18, 2015)

when it happens again also check the spark.......


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## semipro (Jun 18, 2015)

I have noticed that many fuel filters never "fill" and that fuel will still flow through fine even though air is trapped inside.


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## begreen (Jun 18, 2015)

The mower runs great and starts right up again if I wait 10 secs for the fuel filter to refill. I'm going to replace the filter with one from Kohler that lists for this motor. I note that this is a 51 micron filter. Some are as fine as 15 micron.


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## rustynut (Jun 18, 2015)

also had one that had heat shields fallen off and when the temp & humidity was just right the carb would frost up and get real silly to the point you would stop driving it. Then after a while while you were scratching your head it would thaw out and things would be fine......until the next time weeks later.......that was a tough find
rn


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## begreen (Jun 20, 2015)

Until I can get the proper 51 micron Kohler filter I will just fill the tank. I did that last night and cut tall grass for an hour in our hilly side field. The mower ran like a charm and still had 1/2 tank left.

On a different but even worse note my splitter won't run for more than a minute. It has a Honda 5hp motor. I pulled the sediment bowl off the fuel valve and it is just filling a drop at a time. Ugh, this one does not look like fun to take apart. Anyone know of any tricks? Is this a case for Seafoam?


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## blades (Jun 21, 2015)

well if it isn't draining from the tank through the filterthen replace the lines and clean the tank with solvent.

Just had  another mystery mower problem - big commercial zero turn about 7 years old- just had it in shop last week for a frozen clutch and the week before for a blown fuse( didn't know at the time of the fuse that it was a symptom of the clutch going out , I just fix them don't run them) anyway customer calls up mower hesitating sometimes dying out doesn't seem to respond to throttle or is late to the party, course he tells it's fuel injected ( no its carbed) anyway after a bit of looking 2 of the 4 bolts that hold the carb and intake assembly on are missing in action and the other two are loose ( factory install never been apart) - hence massive air leak- cause of problem. What rattled those bolts ( 8mm dia x about 3" long)  loose and out no idea , unless not installed correctly to begin with.


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## johninwi (Jun 21, 2015)

Assuming the outlet is toward the front of the tank, is the motor is running rough by chance? might be if it's running rough and the tank is being shaken more then the fuel is "bouncing " around inside and not flowing? The gas is airaited? How do the plugs look? Might be time for a tuneup. Would be a longshot but you've covered everything else.
When you swapped carbs do you set the float so the carb filled completly?
Or maybe just mow the hill first?


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## begreen (Jun 21, 2015)

blades said:


> well if it isn't draining from the tank through the filterthen replace the lines and clean the tank with solvent.
> 
> Just had  another mystery mower problem - big commercial zero turn about 7 years old- just had it in shop last week for a frozen clutch and the week before for a blown fuse( didn't know at the time of the fuse that it was a symptom of the clutch going out , I just fix them don't run them) anyway customer calls up mower hesitating sometimes dying out doesn't seem to respond to throttle or is late to the party, course he tells it's fuel injected ( no its carbed) anyway after a bit of looking 2 of the 4 bolts that hold the carb and intake assembly on are missing in action and the other two are loose ( factory install never been apart) - hence massive air leak- cause of problem. What rattled those bolts ( 8mm dia x about 3" long)  loose and out no idea , unless not installed correctly to begin with.



RE: The Honda GX motor on the splitter. I don't think there is a filter on this tank unless it is at the fuel pickup tube. Could be a screen there but it would have to be tiny. The pickup tube looks to be about 4mm across. What solvent is safe to use for the tank and hoses, yet effective.

@johninwi as long as there is fuel the motor runs fine, it just isn't getting the fuel fast enough.  I comes out at about a drop every 2 seconds out of the fuel shut off valve if the sediment bowl is removed.


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## maple1 (Jun 22, 2015)

begreen said:


> On a different but even worse note my splitter won't run for more than a minute. It has a Honda 5hp motor. I pulled the sediment bowl off the fuel valve and it is just filling a drop at a time. Ugh, this one does not look like fun to take apart. Anyone know of any tricks? Is this a case for Seafoam?


 
Is the fuel valve/bowl (petcock?) removeable? If so, time to do that. There may be a screen on there inside the tank that's plugged or gummed up. One of the kids motorbikes had that happen a couple years ago - it was nasty in there.

Seafoam is usually my first try when things like this happen - that way at least it'll clean things up some for when you have to take things apart if it doesn't work, and it's easy to do. But when it's a total or near total blockage, I usually go right to taking things apart.


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## begreen (Jun 22, 2015)

It looks like the valve is integral with the carburetor. I'll get some seafoam today.


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## begreen (Jun 22, 2015)

I bit the bullet and got to work on the splitter today. The grass is browning out and can wait until Sept. at this rate.

I narrowed the issue down to the fuel shut off valve. Fuel flowed freely from the tank out of the fuel delivery hose. I took apart the valve and found a bit of varnish built up under the rubber valve seat. I carefully scraped it out with an awl, then carb cleaned it, scraped again, cleaned again until there was no more residue. I also carb cleaned and wiped the rubber valve seat clean a few times. Put it together and I was now getting about 3 drops a second heading into the sediment bowl instead of a drop every 2 seconds. Put it back together and it definitely ran better and longer. Only stalled once, so I added an ounce of Seafoam to the tank and ran it for another 30 minutes. Seems fine, I split up a bunch of alder and wild cherry without a sweat and no more stalling. At the end of this splitting season I will add another ounce of Seafoam to the last tank and will run the tank dry.


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## jebatty (Jun 23, 2015)

Had the same issue with my wood splitter and a small B&S engine, gravity feed, no fuel filter. Never solved the problem other than keeping the fuel tank full.


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## maple1 (Jun 23, 2015)

begreen said:


> I bit the bullet and got to work on the splitter today. The grass is browning out and can wait until Sept. at this rate.
> 
> I narrowed the issue down to the fuel shut off valve. Fuel flowed freely from the tank out of the fuel delivery hose. I took apart the valve and found a bit of varnish built up under the rubber valve seat. I carefully scraped it out with an awl, then carb cleaned it, scraped again, cleaned again until there was no more residue. I also carb cleaned and wiped the rubber valve seat clean a few times. Put it together and I was now getting about 3 drops a second heading into the sediment bowl instead of a drop every 2 seconds. Put it back together and it definitely ran better and longer. Only stalled once, so I added an ounce of Seafoam to the tank and ran it for another 30 minutes. Seems fine, I split up a bunch of alder and wild cherry without a sweat and no more stalling. At the end of this splitting season I will add another ounce of Seafoam to the last tank and will run the tank dry.


 
So - I wonder if there's a correlation to your mower problem? Two motors same fuel? Could be some varnish buildup on the mower tank outlet that is restricting fuel just enough when there is not enough fuel in the tank above it (head) to push it through?

From my experience with it, a varnish problem is just the thing Seafoam is made for.

(Also, not sure it's proper or not, but when I'm pretty sure I have some varnish/buildup that needs cleaning out, I usually double up the prescribed Seafoam ratio for the first tank through).


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## semipro (Jun 23, 2015)

Interesting info on Seafoam here: http://hildstrom.com/projects/seafoam/
Its about $60/gal. off the retail shelf.


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## sportbikerider78 (Jun 23, 2015)

begreen said:


> I bit the bullet and got to work on the splitter today. The grass is browning out and can wait until Sept. at this rate.
> 
> I narrowed the issue down to the fuel shut off valve. Fuel flowed freely from the tank out of the fuel delivery hose. I took apart the valve and found a bit of varnish built up under the rubber valve seat. I carefully scraped it out with an awl, then carb cleaned it, scraped again, cleaned again until there was no more residue. I also carb cleaned and wiped the rubber valve seat clean a few times. Put it together and I was now getting about 3 drops a second heading into the sediment bowl instead of a drop every 2 seconds. Put it back together and it definitely ran better and longer. Only stalled once, so I added an ounce of Seafoam to the tank and ran it for another 30 minutes. Seems fine, I split up a bunch of alder and wild cherry without a sweat and no more stalling. At the end of this splitting season I will add another ounce of Seafoam to the last tank and will run the tank dry.



Leaving a tank dry is a great way to get condensation and rust.  Get some ethanol free gas if you can get it.  Add some stabilizer and fill the tank to the brim.  

With stabilizer, gas is good for at least 6 months.  

I have stored motorcycles with full metal tanks for up to 2 years using this method.  Zero issues.


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## Highbeam (Jun 24, 2015)

sportbikerider78 said:


> With stabilizer, gas is good for at least 6 months.
> I have stored motorcycles with full metal tanks for up to 2 years using this method.  Zero issues.



Me too. Tank full of stabilized gas for storage. If equipped with a fuel shutoff valve I shut it off and run the carb out. Then roll the piston to TDC and leave it dormant.


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## begreen (Jun 24, 2015)

Good to know, thanks. Only the splitter tank is metal and I may go a year before using it again. All the others are plastic. I put stabilizer in the mower tank, but run the trimmer and leaf blower (2 cycle) dry.


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## begreen (Jun 27, 2015)

Ran the splitter for a couple hours today. I think it is running better now than it has for the past couple years. The motor purred like a kitten no matter the load. It looks like the shutoff valve cleaning plus seafoam treatment really worked!


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