Bobcat 743 fuel pump

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Kilgour Frams

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My 743 will not start. I have checked the fuel line, filter, primer bulb etc.. all clear. I detached the fuel lines from the pump and hooked the in flow to a can of fuel, cranked the engine and no fuel came out. I went a bought a new fuel pump and did the same with the same results no fuel. I took the old fuel pump and hooked a line to the in flow and put the end in a can of fuel. I pressed the pump against a hard surface a fuel came out of the out flow. I think I narrowed it down to a worn cam shaft to the pump. I want to hook up an electric pump and was wondering what psi pump I should get, I believe the fuel volume is 11gpm. Any help would be appreciated. Kilgour Farms
 

Tazza

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The hydraulic flow is 11GPM fuel is very low, any automotive fuel pump will do just fine. I would seriously doubt the cam is worn enough to cause issues. I'd suspect gelled fuel first, as you replaced the pump with a known good one.
Will it start if you hold pressure on the primer bulb while cranking?
Ensure the stop cable is not pulled up and that the arm on the side of the engine is not in the stop position.
 
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Kilgour Frams

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The hydraulic flow is 11GPM fuel is very low, any automotive fuel pump will do just fine. I would seriously doubt the cam is worn enough to cause issues. I'd suspect gelled fuel first, as you replaced the pump with a known good one.
Will it start if you hold pressure on the primer bulb while cranking?
Ensure the stop cable is not pulled up and that the arm on the side of the engine is not in the stop position.
After cranking it for a while it will start the run for a few minutes then stall. I have a feeling that the cam is still pumping but not pushing the cylinder far enough at the rate required to sustain the flow. I replaced a line, cleaned the fuel thank, replaced filter, hand primer, lines, etc.. It all points to the fuel pump. The old one works fine when pressure is applied to it out of the housing. as well as the new one, when put back in they won't pump. Thats what leads me to believe its cam shaft. I figured that if I use an electric pump I can bypass the problem with the fuel pump?
 

skidsteer.ca

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After cranking it for a while it will start the run for a few minutes then stall. I have a feeling that the cam is still pumping but not pushing the cylinder far enough at the rate required to sustain the flow. I replaced a line, cleaned the fuel thank, replaced filter, hand primer, lines, etc.. It all points to the fuel pump. The old one works fine when pressure is applied to it out of the housing. as well as the new one, when put back in they won't pump. Thats what leads me to believe its cam shaft. I figured that if I use an electric pump I can bypass the problem with the fuel pump?
You did check the pickup tube inside the tank as there are know to crack and fall off, only picking up fuel with a full tank.
You can use a electric pump if you want. Just don't get one with too much fuel pressure, say 5 to 7 psi
Ken
 

Tazza

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You did check the pickup tube inside the tank as there are know to crack and fall off, only picking up fuel with a full tank.
You can use a electric pump if you want. Just don't get one with too much fuel pressure, say 5 to 7 psi
Ken
That sympton is exactly what happens if you don't screw the bleed screw all the way back in. Ensure its fullyturned off or the fuel pressure generated simply goes back to the fuel tank.
 
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Kilgour Frams

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That sympton is exactly what happens if you don't screw the bleed screw all the way back in. Ensure its fullyturned off or the fuel pressure generated simply goes back to the fuel tank.
I guess my question would be that I detached the fuel hose from the pump both in-flow and out-flow. I then hook an external hose to both. I the put the in-flwe hose in a pail of fuel and cranked the engine over. Should this not have pulled fuel through the pump and out the out-flow tube? The out flow tube was placed in another can to see if fuel would go through which I didn't. If the pump was working properly it should have let the fuel flow through, correct? The bleed screw is tight. Both tubes in the tank have been replaced.
 

ddsprint

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I guess my question would be that I detached the fuel hose from the pump both in-flow and out-flow. I then hook an external hose to both. I the put the in-flwe hose in a pail of fuel and cranked the engine over. Should this not have pulled fuel through the pump and out the out-flow tube? The out flow tube was placed in another can to see if fuel would go through which I didn't. If the pump was working properly it should have let the fuel flow through, correct? The bleed screw is tight. Both tubes in the tank have been replaced.
you are most likely getting air in the system somewhere, may have a cracked line best way to check fuel working or not, is to crack the first injector, you will see if it is working or not, when it works it will push some fuel out and this is best way to bleed the system, part of the problem you are running into is that you keeping taking it apart, this is alright although to bleed one of these systems can piss one off, in meaning is there air still in there or this a different problem, it is gravity feed until it gets to the syphon pump, one this machine starts to run crack first injector and repump the ball the machine will still run, don't give up it is a diesel and it will send you in circles so keep spinning with them, you will figure it out, hope this helps, don't quit
 

Tazza

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you are most likely getting air in the system somewhere, may have a cracked line best way to check fuel working or not, is to crack the first injector, you will see if it is working or not, when it works it will push some fuel out and this is best way to bleed the system, part of the problem you are running into is that you keeping taking it apart, this is alright although to bleed one of these systems can piss one off, in meaning is there air still in there or this a different problem, it is gravity feed until it gets to the syphon pump, one this machine starts to run crack first injector and repump the ball the machine will still run, don't give up it is a diesel and it will send you in circles so keep spinning with them, you will figure it out, hope this helps, don't quit
Using an external source of fuel is fine but you NEED to prime the system. Don't rely on the lift pump having enough suction to draw the fuel up on its own. Its made to move fuel, not suck air till it gets to fuel. Prime it and then do what you said, see if fuel is squirted out. Also when primed ensure you have a bit of a restriction on the end as if your one way valve is bad you will loose prime.
If you still believe its the lift pump, give the primer bulb a squeeze and get someone to crank the engine. If it dies every time you let go of the primer bulb its a sign that you have a bad lift pump or plugged filter/hose.
 

rosalia

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Mar 19, 2023
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My 743 will not start. I have checked the fuel line, filter, primer bulb etc.. all clear. I detached the fuel lines from the pump and hooked the in flow to a can of fuel, cranked the engine and no fuel came out. I went a bought a new fuel pump and did the same with the same results no fuel. I took the old fuel pump and hooked a line to the in flow and put the end in a can of fuel. I pressed the pump against a hard surface a fuel came out of the out flow. I think I narrowed it down to a worn cam shaft to the pump. I want to hook up an electric pump and was wondering what psi pump I should get, I believe the fuel volume is 11gpm. Any help would be appreciated. Kilgour Farms
i have seen the fuel shut off resticked do the same thing
 
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