753 fuel pickup tube

[reaperman]

Im looking for a bit of input on a minor issue Im pretty sure I figured out.

About 2 months ago I was lucky to have had my pickup tube fall off when and where it did. It happened close to my house and the weather was very nice for a Minnesota November day. I was lucky again to find a replacement on Amazon with next day delivery which was a Sunday. One week later the weather turned nasty cold and we had 8" of snow. I was so thankful the tube hadn't fallen off then instead.

The replacement of the tube is fairly straightforward on my machine since it's at least visible and not bad to access. The tube kit came standard with a 12" tube and check valve and a couple clamps. It appears all kits come standard with the 12" tube to fit a variety of bobcat models. When installing the tube and check valve I noticed the 12" tube hit the bottom of the fuel tank about 7 or 8" down. I wasn't sure at that point if I should keep pushing the tube all the way in. Wondering if its a bad idea for the bottom the the tube/check valve to sit right of the bottom or not. Well I pushed it all the way in rather than trimming the top off and finished up. Bled the filter and the machine fired right up as usual. Drove around a bit and everything was good.

The following week it snowed so I plugged in my machine a few hrs before hand. When I started the machine, it ran about 2 seconds and died. That's the first time it had ever skipped a beat. I started it up again, it cranked a bit and fired right up and ran perfect for about 2 hrs as I plowed. The next time I went to use the machine after a cold spell was over, I plugged it in for a while like usual. I went to start it and it fired and died again. A few more attempts and it was running, I could tell it wasn't running on all cylinders right away but in a few seconds it was purring along. Again, this machine has always started right up without a hitch. I always wait for the glow plugs to cycle. Again this happened a few day ago where it would take 5-6 attempts before it was running. I was initially thinking a glow plus or two maybe bad. I removed all 4 and tested them and they all glow top to bottom, no issue. I installed the plugs and tried to start the machine, same result. It would fire quickly and die, then just swing over. So now Im pretty sure the issue is fuel delivery. I loosened the air bleeder screw on the filter and I had to squeeze the ball about 2 or 3 times before fuel would start to come out. Once it did, I hit the key and it started right up.

So, I'm guessing some fuel is slowly leaking past the check valve inside of the tank and creating air in the filter. Im wondering, being the check valve is laying on its side on the bottom of the tank. If that would allow some fuel to leak past vs a check valve that would be sitting strait up and down if I shortened the pickup tube. I didnt pop the hood to see where the fuel line from the filter connects to the top of the pickup tube L-fitting. Im assuming that ones tight since it's fastened with a hose clamp. I'm still leaning towards them $13 Chinese pickup tube with the convenient one day delivery as the issue. So I will be getting a different check valve. But Im wondering if its a good or bad idea to shorten the pickup tube to where I cut it off at the point where it hits the bottom of the tank rather than push it in another 4 or so inches. Thanks

 

[brdgbldr]

Im looking for a bit of input on a minor issue Im pretty sure I figured out.

About 2 months ago I was lucky to have had my pickup tube fall off when and where it did. It happened close to my house and the weather was very nice for a Minnesota November day. I was lucky again to find a replacement on Amazon with next day delivery which was a Sunday. One week later the weather turned nasty cold and we had 8" of snow. I was so thankful the tube hadn't fallen off then instead.

The replacement of the tube is fairly straightforward on my machine since it's at least visible and not bad to access. The tube kit came standard with a 12" tube and check valve and a couple clamps. It appears all kits come standard with the 12" tube to fit a variety of bobcat models. When installing the tube and check valve I noticed the 12" tube hit the bottom of the fuel tank about 7 or 8" down. I wasn't sure at that point if I should keep pushing the tube all the way in. Wondering if its a bad idea for the bottom the the tube/check valve to sit right of the bottom or not. Well I pushed it all the way in rather than trimming the top off and finished up. Bled the filter and the machine fired right up as usual. Drove around a bit and everything was good.

The following week it snowed so I plugged in my machine a few hrs before hand. When I started the machine, it ran about 2 seconds and died. That's the first time it had ever skipped a beat. I started it up again, it cranked a bit and fired right up and ran perfect for about 2 hrs as I plowed. The next time I went to use the machine after a cold spell was over, I plugged it in for a while like usual. I went to start it and it fired and died again. A few more attempts and it was running, I could tell it wasn't running on all cylinders right away but in a few seconds it was purring along. Again, this machine has always started right up without a hitch. I always wait for the glow plugs to cycle. Again this happened a few day ago where it would take 5-6 attempts before it was running. I was initially thinking a glow plus or two maybe bad. I removed all 4 and tested them and they all glow top to bottom, no issue. I installed the plugs and tried to start the machine, same result. It would fire quickly and die, then just swing over. So now Im pretty sure the issue is fuel delivery. I loosened the air bleeder screw on the filter and I had to squeeze the ball about 2 or 3 times before fuel would start to come out. Once it did, I hit the key and it started right up.

So, I'm guessing some fuel is slowly leaking past the check valve inside of the tank and creating air in the filter. Im wondering, being the check valve is laying on its side on the bottom of the tank. If that would allow some fuel to leak past vs a check valve that would be sitting strait up and down if I shortened the pickup tube. I didnt pop the hood to see where the fuel line from the filter connects to the top of the pickup tube L-fitting. Im assuming that ones tight since it's fastened with a hose clamp. I'm still leaning towards them $13 Chinese pickup tube with the convenient one day delivery as the issue. So I will be getting a different check valve. But Im wondering if its a good or bad idea to shorten the pickup tube to where I cut it off at the point where it hits the bottom of the tank rather than push it in another 4 or so inches. Thanks

One problem I’ve had in the past with a fuel tube that was not too long but was actually curling up and sucking air from the top of the fuel instead of staying on the bottom.

The other thing is that your primer ball should have a check valve inside of it also that should keep the fuel from draining back. If it were me I would go ahead and replace the primer ball since it is easier to replace then the fuel pickup screen and see if that fixes the issue.

Are you sure you don’t have a bad fuel line connection? If you just have a small hole sucking air you will have this problem. A line may have cracked when you were working on it.

The newer Bobcats do not use the fuel line screen /“check valves” anymore( I’m not even sure that these are really meant to be a real fuel check valve). They just depend on the primer bulb check. Not saying that this isn’t your issue, but could be other things also.

I have some new old stock of the Bobcat fuel line screen valves if you can’t find one. Just let me know and I can try to dig one out of my parts bin.

 

[reaperman]

One problem I’ve had in the past with a fuel tube that was not too long but was actually curling up and sucking air from the top of the fuel instead of staying on the bottom.

The other thing is that your primer ball should have a check valve inside of it also that should keep the fuel from draining back. If it were me I would go ahead and replace the primer ball since it is easier to replace then the fuel pickup screen and see if that fixes the issue.

Are you sure you don’t have a bad fuel line connection? If you just have a small hole sucking air you will have this problem. A line may have cracked when you were working on it.

The newer Bobcats do not use the fuel line screen /“check valves” anymore( I’m not even sure that these are really meant to be a real fuel check valve). They just depend on the primer bulb check. Not saying that this isn’t your issue, but could be other things also.

I have some new old stock of the Bobcat fuel line screen valves if you can’t find one. Just let me know and I can try to dig one out of my parts bin.

Thanks much for the input. This morning I loosened the bleeder screw and squeezed the bulb and fuel immediately came out. I had no intention on starting the machine. Rather I wanted to see if anything leaked back, I guess it didnt. This is one thing I havent tried yet before starting the machine since changing the tube. Its only 5 degrees here and my machine sits in my uninsulated pole building. So for testing different things now its really isnt the best of times.

Im wondering if there isnt an issue other than the machine being cold. The time I did plug it in, it wasnt plugged in very long before I went to start it. However, it must be sucking a little air when the engine first fires, runs for a second or so and dies. When the tube broke off, I changed the fuel filter right away since I always have one on hand. In hopes of that being an easy fix rather than the pickup tube. So the filer is new. And once running, it runs as usual, no issues. I probably have 5-6 hours plowing snow since changing the tube.

Another thought is the battery. Maybe its not cranking as strong. I just thought of this and I have a load tester I will throw on it to see. Ive had this battery for a long time, a OEM Bobcat brand. I'm guessing its at least 8 yrs old. It should be replaced, this time of year especially. Even more so for a machine that isnt run very much and sits in sub zero temps for extended periods of time.

Back to the tube. Its interesting you say you had one curl around, it makes sense. I just assume mine was on the bottom. Before I replaced mine, I put it in hot water to soften and take the curl out of it and make sure it was strait. Im sure they just cut a piece off a large roll so it has memory. Then I was surprised it bottomed out earlier than expected. But if its one size fits all. My machine has a smaller tank than alot of bigger machines so I assume their tanks are deeper. I think I could shorten the tube without removing the grommet it I can pull the L fitting thru the top and cut it when I feel the check valve hit the bottom. I most likely wont do a whole lot now being its the coldest time of year. Im confident I can get it started to plow snow. I just need to plug it in overnight so its good and warm. But I will test the battery.

Thoughts?

 

[brdgbldr]

Thanks much for the input. This morning I loosened the bleeder screw and squeezed the bulb and fuel immediately came out. I had no intention on starting the machine. Rather I wanted to see if anything leaked back, I guess it didnt. This is one thing I havent tried yet before starting the machine since changing the tube. Its only 5 degrees here and my machine sits in my uninsulated pole building. So for testing different things now its really isnt the best of times.

Im wondering if there isnt an issue other than the machine being cold. The time I did plug it in, it wasnt plugged in very long before I went to start it. However, it must be sucking a little air when the engine first fires, runs for a second or so and dies. When the tube broke off, I changed the fuel filter right away since I always have one on hand. In hopes of that being an easy fix rather than the pickup tube. So the filer is new. And once running, it runs as usual, no issues. I probably have 5-6 hours plowing snow since changing the tube.

Another thought is the battery. Maybe its not cranking as strong. I just thought of this and I have a load tester I will throw on it to see. Ive had this battery for a long time, a OEM Bobcat brand. I'm guessing its at least 8 yrs old. It should be replaced, this time of year especially. Even more so for a machine that isnt run very much and sits in sub zero temps for extended periods of time.

Back to the tube. Its interesting you say you had one curl around, it makes sense. I just assume mine was on the bottom. Before I replaced mine, I put it in hot water to soften and take the curl out of it and make sure it was strait. Im sure they just cut a piece off a large roll so it has memory. Then I was surprised it bottomed out earlier than expected. But if its one size fits all. My machine has a smaller tank than alot of bigger machines so I assume their tanks are deeper. I think I could shorten the tube without removing the grommet it I can pull the L fitting thru the top and cut it when I feel the check valve hit the bottom. I most likely wont do a whole lot now being its the coldest time of year. Im confident I can get it started to plow snow. I just need to plug it in overnight so its good and warm. But I will test the battery.

Thoughts?

Here is a video of a fuel pickup tube replacement on a 763. You can compare the length that he uses to what you have. He also talks about how the 90 deg. fitting could get debris in it and cause a fuel starvation problem. The fuel pickup tube starts at about 5 minuets in. He also shows how to properly bleed the air out of the system before firing up the machine. This guy is the go to for any Bobcat issues.


Here is also a link to the parts manual. The schematics may give you a better idea as to the proper length also:
https://partscatalog.bobcat.com/

On my old 742 the fuel pickup was meant to lay on the bottom of the tank so the lines were pretty long. But on the 753 that does not look to be the case but it should not really affect it.

Replacing the fuel filter could be your air issue if you didn’t get all of the air out of the filter before trying to start the machine. I always pump out the air with the primer bulb while tapping the filter and then wait a few minutes and repeat.

 

[reaperman]

Thanks again. I called the local dealer and asked about the tube length. He said its meant to lay on the bottom of the tank so it will follow the fuel going up or down hills, etc. I hadnt thought of that, so the length is standard at 12". I also watched the YT video in the past knowing my day would come. I also watched it before I changed the tube. I love this guy, I owe him a beer or two. IF I recall, he mentioned the check valve should be installed to prevent drain-back. And I did blow air thru the L connector.

I load tested the battery and according to my analog gauge its doing what it should. On the fuel filter, I've changed dozens over the years at work. Some can be fussy, but it helps to have a second person priming the bulb for a while as the engine is getting started right after the replacement. I would think the air has purged since I have a half dozen or so hrs on it. However, I should make sure its spun on tight. Whatever the issue, if there actually is one cant be too complicated since it runs great once started. Great running diesels can still be a pain to get running in cold weather. I have no idea when I will use my machine again. But when I do, I will make sure its plugged in for a long time as I normally do. These past few times, that wasnt the case.

 

[Zeke67]

Try replacing your fuel pump. My 753 had similar symptoms. It would either start and run great or start then die. New fuel pump cured it.

 

[PistonPete]

I think you're right on the track with the fuel problem. When you have to prime the bulb again after it sits, that's a dead giveaway that fuel is draining back and letting air in the line. You did the right thing checking the glow plugs first, though!

I had a similar thing happen on my old skid steer. It would start right up, run for a few seconds, and then die. Drove me crazy. For me, it turned out to be a tiny crack in the fuel line right before the filter. It was so small you couldn't see it, but it was letting just enough air in overnight to cause a headache.

If I were you, I would definitely shorten that pickup tube. I agree with you, I don't think that check valve is designed to work lying on its side. It probably can't seal right. And yeah, I'd be suspicious of that cheap Amazon part, too.

If it were my machine, I'd trim the tube first since that's a free fix. If it still acts up, I bet a new, better quality check valve will solve it for good.

Hope you get it figured out!

 

[reaperman]

Try replacing your fuel pump. My 753 had similar symptoms. It would either start and run great or start then die. New fuel pump cured it.

Thanks, the lift pump crossed my mind. It's still the original so it's likely 25 years old so a new one wouldn't hurt. Otherwise my machine is in good shape with only 1400 hrs.

 

[reaperman]

Try replacing your fuel pump. My 753 had similar symptoms. It would either start and run great or start then die. New fuel pump cured it.

I just came across this from a previous post that makes sense.

The lifting pump has a rubber membrane that expands when heated when it is old and can not pump fuel. When did you do the test with a separate ken and electric pump where did you tighten the hose from the electric pump? On the lifting pump or directly on the injection pump? If it tied it to the lifting pump, the membrane actually limits fuel flow form electric pump. A solenoid that opens when heated is not available unless your machine is equipped with a BOSS, but in this case it should display an error on the screen.It may be a shut off solenoid with a partially distorted isolation between the bobbin windings, and upon solenoid heating it gives a partial short and relaxes a little stop lever.

 

[reaperman]

.

The other thing is that your primer ball should have a check valve inside of it also that should keep the fuel from draining back. If it were me I would go ahead and replace the primer ball since it is easier to replace then the fuel pickup screen and see if that fixes the issue.

Are you sure you don’t have a bad fuel line connection? If you just have a small hole sucking air you will have this problem. A line may have cracked when you were working on it.

I havent done any troubleshooting yet because the weather here is sub zero well thru the 10 day forecast. Anyway, you mention the primer bulb should have a check valve also. Which brings up a thought. If the chinese check valve in the tank isnt working, and the primer bulb valve is. Wouldnt that explain the machine running for a couple of seconds, then getting a shot of air and dying? I followed the fuel path. Tank to primer bulb (fuel held by the check valve)--bulb to lift pump--lift pump to filter--filter to injectors. The bulb would hold all of the fuel for everything except the line coming from tank. So the machine would be able to start. Then the lift pump would see a shot of air and couldnt push fuel to the engine and create a void in the fuel filter. Which makes be believe it still may be the the pickup tube check valve??