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Discussion Starter · #1 ·
I was mowing today with my 442, (orig. 12 hp Kohler) when my tractor acted like it was running low on fuel. It didn't shut off, but it wouldn't stay on speed, lost power, etc. The gas tank had what looked like 2 or 3 inches in it..

I stopped and played with it for a while and found:
1. It has a transparent fuel filter between pump and carb. That filter normally sits about half full, but it was now sitting mostly empty: (It has a 1" high "cylinder" which should sit full of fuel. But it had about 1/8" of fuel, the rest air.)
2. The fuel that was in the filter was bubbling, looked exactly like boiling water.
3. If I put the choke on a little bit, it helped the engine run better. At about half-choke, it seemed to run fine.
4. I let it cool down and then pulled the fuel hose off of the pump outlet. Turned the engine over a couple times, and fuel spurted out a couple times.
5. On a whim, I filled the fuel tank to the top. Now that I did that, the fuel filter is now full, and the engine is now running fine again, without choke.
But it does still have lots of foamy-looking air bubbles in the fuel filter.

Anybody recognize this? It runs fine on a full tank, but as the tank gets down around a 1/3 or 14 tank, it acts like it's not getting fuel.
Fuel pump? Clogged filter in the tank?

Thanks in advance,

Bob
 

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When you fill the tank, you are increasing the amount of pressure on the fuel that is leaving the fuel tank. This principle is used in municipal water systems by building water towers or constructing huge water tanks in an area that is much higher than the rest of the town.


So.... what's the real problem here?


- a weak fuel pump can cause this because it may be having a harder time sucking fuel from a tank that is close to empty.

- however, you mention bubbles and that makes me think that you have a fuel line issue between the tank and the pump. It might be that the line has become porous from age or it might be that it is so hardened from age that the clamps cannot squeeze the rubber hose tight enough to make a good seal at either the tank end or the pump end or both ends. Air is being sucked into the line at these points.

Your tractor is at least 40 years old. If I were you, I would go and buy a new length of 1/4" neoprene fuel hose and then install it Remove the seat, fenders etc to get to the fuel tank. Take the hose off the fuel pump, stick it into a proper fuel can and let it drain. Remove anything that is holding that fuel line to other hoses or the frame and then pull the tank out. Inside the tank is a fuel screen. Do what you have to and destroy that screen so that it does not cause you problems in the future and that you eliminate a possible source of the current problem. Install the new hose on the tank and reuse the existing spring clamp because those are superior to gear clamps in this application. Put a small bolt in the open end of the fuel line to seal it off while you thread the new hose back under the frame. Install the fuel tank, fenders, seat and so forth and then ziptie the new hose as needed to keep it out of harm's way. The last thing you do is cut the new hose to the proper length but leave a bit of slack in case you have to shorten the end of it a bit in the future.

Connect the hose to the fuel pump inlet using another spring clamp and not a gear clamp. Refill the gas tank and start the engine. Did the bubbles go away?
 

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The cost involved to replace the line is negligible. By servicing the fuel tank, removing the screen and replacing all of the fuel lines, you take several suspects out of the equation. If you still have the problem after doing those things, then the pump becomes the most likely suspect.
 

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Be sure new hose you buy can handle E10 fuel......if not, you'll be doing it again very soon.....replace filter too and be sure it can handle E10. Be sure tank does not have a screen in outlet....after 40 yrs it may need cleaning. Bob M
 

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Discussion Starter · #6 ·
Well, you nailed it. The old fuel line was dessicated and cracked right where it ran past the lower block. Once I cut the old hose off and was able to hold it and inspect it, it was obvious.

I replaced the line and removed the screen.

I bought the hose at the hardware store and it's stamped "Fuel Hose" so I presume it's rated for whatever methanols/ethanols, etc.

Bob
 

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Bob, did you replace the fuel filter with a correct replacement as well? If not then I suggest you order one up. While you're at it you might as well give your sweetheart a tune up. She will love you for that.
 

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Discussion Starter · #8 ·
Filled up the tank and ran for the first time today (since the new fuel line)

Started and ran fine, the filter seemed to sit a little fuller. But I still have to have the choke about halfway on for the engine to run. So something's amiss.

I can guarantee that there are no fuel obstructions at least to the point of the pump inlet.

Anyway, I mowed for a while and it seemed to lose power. I had a look and my filter is sitting empty again. And the gas is bubbling.

I was googling electric fuel pumps, and I came across a page mentioning vaporlock being a potential problem on GT's in general due to heat from the muffler. I will say that this area feels like it's absolutely cooking from the muffler. Of course if I'm running with choke on, I might be running rich, too. I don't know. But the bubbling in the gas, and the fact that it really worsens after about 20 minutes of mowing really makes me think it might be vaporlock.

1. On a 442, is there supposed to be some kind of heat shield between the muffler and fuelpump/carb area? My muffler is single-walled, and there's nothing at all between there and the fuelpump/carb.
2. I'm inclined to go the route of an electric fuel pump: they're cheaper than the stock part, and I think do a better job. Advice?
3. Of course I could just run the exhaust vertical up through the hood, and that might solve this problem.... :sidelaugh:
4. "Case 220/4" mentioned "the correct fuel filter"... does it really matter? Shouldn't any smallish fuel filter be fine?

Thanks again,

Bob
 

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Bob,
I think that you will agree that your engine should not have to run on half-choke. That tells me that you are running way too lean. WHY? That's the next question to address.


What condition are the throttle shaft and shaft bushings in? If that shaft is flopping around, then air is leaking around the shaft and upsetting the fuel mixture balance. Another place to look is the gasket that goes between the carb and the block. If it is damaged or the carb is not bolted tightly, then that will contribute.

You also may have dirt in the passages of the carb that are preventing fuel from being vaporized, thus leaning out the mixture.

I agree that vapour lock MAY be the root cause here but if the exhaust system is correct (meaning OEM), then I would be looking elsewhere. Many thousands of these engines run just fine so why not yours? Of course it also might be a weak fuel pump and replacing it with an electric pump may prove to be the final solution. Doing that may cure your half-choke issue too if the pump is so weak it cannot keep the float bowl full at all times. One way to check the problem would be to gravity feed fuel directly to the carb from a fuel tank borrowed from another engine such as an old push mower.

It's an old tractor Bob.... lot's of small things can go wrong but most of them are peanuts to repair money-wise. The carb can be re-bushed and a new throttle shaft installed. A new carb/block gasket is readily available. Sometimes, it isn't just one thing but an accumulation of several small things. Anything you do, likely needs to be done anyway.... such as replacing that fuel line that you did not realize was about to cause problems anyway. Knock each one of these problems off and you will eventually resolve this.
 

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Discussion Starter · #10 ·
Thanks for the input.

I intend to clean out and inspect the carb off my K301 Cub Cadet engine, and then try that one.
I'll also do the gravity feed and see if that helps.

If it does, I'm definitely going to do the elec. fuel pump, probably an in-tank pump. If I do it, I'll document as I go.

I'm still inclined to consider heat-shielding on the exhaust, something like you'd find above your car's catalytic converter....

Bob
 

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I think that an "In-tank" pump would bring special challenges that are not needed. I agree that a pump mounted almost directly under the tank is a good idea because it provides the pump with a "flooded inlet" and pumps do well pushing fuel.

The gravity test would tell you almost immediately if the engine can now be run with no choking, so that is the first test I would try. That would tell you whether you need to pursue remedial action with the carb.

In truth, the heat shield should not be needed BUT................with the crap that is being delivered from the pump nozzle these days, it could be that the "modern" fuel is more prone to vapour lock than the "real fuel" used when the engines were still being installed in the tractors.

I would like you to find the true problem here and not just some band-aid that masks the real problem.
 

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Describe the bubbles - are they moving in the direction towards the engine while running and after it is shut off? Get enough vacuum going and it will get through some pretty small openings. My guess is if you are sucking in some air while and after running your pump is still good. Did you buy the black rubber fuel hose or the 'clear' plastic fuel line?

Do you have the right cap on the tank? Is the vent clear?

I will say that I removed my tank a few weeks ago, cleaned it inside and out to paint it. Put it back on with new 3/8" Fuel Hose (that is what was on it and that is what fits the barbs at each end. Filled it to about 1/4 tank. Cranked and cranked and couldnt get fuel to the pump. I blew into the tank and still nothing cam out (this is with all the hose below the tank level). Filled it to 3/4 tank and blew very hard a second time and something finally let loose and no issue since then. I sware the tank and fitting were completely clear but something was up.

There isnt much to rebuilidng these mechanical pumps and cleaning the carbs and reworking them.
 

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Discussion Starter · #13 ·
The bubbles look exactly like boiling water, while the clear fuel filter sits nearly empty. It's definitely worse after it has warmed up.

I used 3/8 black fuel hose, removed the tank, shook it out upside down very thoroughly, etc.

I Removed the remains of the brass screen in the tank outlet elbow. (About half of it was missing/rotted away.)

None of that seemed to help.

Since then I've had a chance to put a fuel tank up on top of the hood and gravity feed fuel into the carb. After 3 or 4 minutes of running, the clear filter still hadn't filled up, and I still couldn't run without choke.

I have an older walbro carb off a Cub Cadet 12 hp Kohler, and I've cleaned it out very well. I'll put that on and see how that does.

As of now I'm thinking my fuel pump is probably fine.

But I still think it's getting too much heat from the exhaust under there.

Bob
 

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Are the bubbles traveling toward the engine/carb/pump while running and afterwards or away?

I honeslty doubt the exhaust is causing the problem as mine is stock and passes in same area and mine runs fine. But...you never know.
 

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And like Hydriv mentioned earlier - make sure you dont have any air leaks at the carb / intake. Spray some carb cleaner around the throttle shaft and base of carb.

Make sure the screen at the flywheel is clean and holes are open for air flow and you have all your tin in place as well.
 

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Discussion Starter · #16 ·
The end of the matter:

I took the Walbro carb from my other K301 engine, and cleaned it out thoroughly.

Installed it with a new gasket, and the engine ran ok, without choke applied. BUT: I had fuel dripping from my fuel pump.

So I took off the pump, took it apart. Found it had a good bit of grit/nastness in it, and someone had added a cork gasket in addition to the rubber membrane that's between the two pump halves. They had put it on the "gasoline" side of the membrane. The cork was what was leaking. I estimated that some kind of extra gasket thickness was needed, so I cut some from paper gasket material, and installed it on the oil side of the membrane. Cleaned out, reassembled, reinstalled. Pulled the plug wire and turned the engine over a little while to squirt/flush out the pump w/ gasoline.

Reassembled, and mowed the whole yard, no problems.

In retrospect, it looks like it must have been running extra-hot because it was running lean. Now that area doesn't seem as hot as it used to, and it's definitely not vapor-locking.

Thanks again for everyone's help and input.

Bob
 

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Bob,
This is a perfect example of what I try to make owners understand about these tractors. Many of them are thirty to forty plus years old and they have been worked on by a variety of people over those years. Some knew what they were doing and some did not. This is one of the reasons why I put all the manuals I could lay my hands on, here at this site because those manuals will tell owners how their tractors and engines were put together at the factory. All too often, it is not the tractor or the engine's fault but rather it is either neglect, wrong parts used or improper repairs that are at the heart of the problem. Once the engine or tractor has been restored to the way it was when it left the factory, the problems miraculously disappear.

Shocking......isn't it? :sidelaugh: :sidelaugh:
 
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