Bobcat 743 Fuel Problems

[theNEWT]

Hi folks. Hopefully someone here might be able to help me in the right direction. I'm not familiar with diesels, so gradually trying to work things out. If someone could explain how the 743 fuel system works I would much appreciate it. It appears to be a gravity fed system somehow. Engine runs for a while then slows, loses power and quits. I might get 5 minutes out of it, sometimes a little more, 10-15min. While operating, the engine seems very good, plenty of power, good idle etc. Sometimes I can coax it back into life with plenty of cranking and gradually raising the revs, but the result is always short lived. At one time, the engine completely refused to start, even the next day. I was stuck out in the open with a pile of logs in the bucket. So... I lifted the canopy to get to things and see things better. Opened the back door, removed the fuel line where it meets the motor, no fuel there. I removed the fuel filter, some fuel inside, the filter looks okay, but I dont know how old it is, so it might be blocked. I used the hand pump to feed fuel into the glass bowl. I opened the air bleed screw and managed to get the engine running, lots of black smoke, as the engine improved I gradually closed the air bleed screw....ran well. What I also found was a second fuel or air line coming from the tank and fitting onto a small pipe at the rear of the engine on the injector rail I guess its called. This pipe seemed quite loose, so before attempting to start the engine, I cut a small piece off the end and used a new clamp. The pipe does seem a little too large for the fitting though, so doing it up tight wasnt easy, especially at the back where it was hard to get to. After starting it ran well for about 15 minutes or so and then began to repeat the power loss symptom, I jumped out, opened the back door and fiddled with the rear pipe while the engine was running....the engine came good. Is this rear pipe the problem? I assume it must pressurize the tank so fuel can flow, or something, I'm not sure. Both pipes feed in at the top of the tank, so clearly the engine must be doing something to create a siphon affect. Any help appreciated.

 

[Tazza]

The fuel system is very simple. You have a pickup tume in the tank, it goes through the hand primer then to the filter. It then goes to the lift pump then to the injector pump. There is a bleed screw that is on the pump where the fuel line connects. There is a small hose that goes to number one injector tap off line. There will be a few more litle hoses to each one to the rear of the head. The last one goes back to the fuel tank. This is just the tap off line, it does nothing but allow internal leakage from the injectors back to the tank.
With that said, there could be multiple issues here. Start with replacing the pickup tube in the fuel tank. Lift the cab, find the elbow to the tank, pull it out and replace the hose with quality fuel line. Replace the fuel filter, they are very cheap if is the CAV style that it should have.
See how you go with that, if it doesn't work, let me know. They are very simple machines.

 

[theNEWT]

The fuel system is very simple. You have a pickup tume in the tank, it goes through the hand primer then to the filter. It then goes to the lift pump then to the injector pump. There is a bleed screw that is on the pump where the fuel line connects. There is a small hose that goes to number one injector tap off line. There will be a few more litle hoses to each one to the rear of the head. The last one goes back to the fuel tank. This is just the tap off line, it does nothing but allow internal leakage from the injectors back to the tank.
With that said, there could be multiple issues here. Start with replacing the pickup tube in the fuel tank. Lift the cab, find the elbow to the tank, pull it out and replace the hose with quality fuel line. Replace the fuel filter, they are very cheap if is the CAV style that it should have.
See how you go with that, if it doesn't work, let me know. They are very simple machines.

Thanks for that. Makes sense. I should also say that the tank did run empty at one stage, never had problems before that, possibly there is air in the system disallowing fuel to be pulled through. I'm not sure what to do with the fuel system once air has entered and I also removed the fuel filter. The previous owner just told me to start it with the air bleed screw open and gradually close it as the engine clears. This did work when I ran it dry. The fuel filter in the glass container after the hand pump is a steel cased filter a little like an oil filter. Is there anything on the end of the fuel line in the tank? Does it have a pickup filter of sorts? I'm not sure what you mean by the 'elbow to the tank'.

 

[Tazza]

Thanks for that. Makes sense. I should also say that the tank did run empty at one stage, never had problems before that, possibly there is air in the system disallowing fuel to be pulled through. I'm not sure what to do with the fuel system once air has entered and I also removed the fuel filter. The previous owner just told me to start it with the air bleed screw open and gradually close it as the engine clears. This did work when I ran it dry. The fuel filter in the glass container after the hand pump is a steel cased filter a little like an oil filter. Is there anything on the end of the fuel line in the tank? Does it have a pickup filter of sorts? I'm not sure what you mean by the 'elbow to the tank'.

There shouuld be a pickup screen with a one way valve in the tank.
To bleed it, you open the bleed screw, squeeze the hand primer till you can feel that there all the bubbles are gone. The fuel just runs back to the tank with the bleed screw open, close it then start the machine.
When you have it bled, all the air should be out. It may not work perfect first time, you may need to do it again, but its rare.

 

[Jrdequipment]

There shouuld be a pickup screen with a one way valve in the tank.
To bleed it, you open the bleed screw, squeeze the hand primer till you can feel that there all the bubbles are gone. The fuel just runs back to the tank with the bleed screw open, close it then start the machine.
When you have it bled, all the air should be out. It may not work perfect first time, you may need to do it again, but its rare.

You may also want to check to see if there was gasoline put into tank. That would let it run for 10 min or so and then power out. You should also check the fuel cap to make sure it is venting. It's 2 easy checks and could save some grief

 

[theNEWT]

You may also want to check to see if there was gasoline put into tank. That would let it run for 10 min or so and then power out. You should also check the fuel cap to make sure it is venting. It's 2 easy checks and could save some grief

Yep, plenty of fuel, about 3/4 full. Venting is a good point too. Something seems to be disallowing fuel through. I cant check until about another week, the machine is on my country block.....I'll see how I go. Thanks for all the advice.

 

[Jrdequipment]

Yep, plenty of fuel, about 3/4 full. Venting is a good point too. Something seems to be disallowing fuel through. I cant check until about another week, the machine is on my country block.....I'll see how I go. Thanks for all the advice.

What I ment was sometimes people accidentally put in gas instead of diesel

 

[theNEWT]

What I ment was sometimes people accidentally put in gas instead of diesel

Oh! No, certainly didnt make that mistake, I can imagine it happening though if one isnt careful. I only ever use one jerry can, the diesel one.. :-D