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I have a bobcat 743, has always ran good and strong untill…

I have a bobcat 743...
I have a bobcat 743, has always ran good and strong untill yesterday. It will start and run cold, but is lacking power and as it gets up to normal operating temp it starts missing and dies. I tried pumping the hand primer when it started this and it seemed to help so I installed an electric fuel pump thinking the old mecanical one died, and by passed stock filter with an inline one, still doing it. It has a manual fuel shut off, and if I clamp off or close the fuel return at the fuel inlet it will kind of run (not good enough to move). Any ideas? what should the fuel inlet pressure/ volume be?
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Answered in 1 hour by:
6/8/2014
Mechanic: Fieldtech59, Shop manager replied 8 years ago
Fieldtech59
Fieldtech59, Shop manager
Category: Construction and Road Equipment
Satisfied Customers: 202
Experience: Construction equipment repair technician since 1986, JLG certified, Shop manager since 2006.
Verified
Hello, the 743 had that two piece CAV filter, I hate those stupid things. You bypassed that filter and fitted an inline, still have the problem. When you fitted the electric fuel pump, you did disconnect from the manual lift pump, right?

The 743 had a fuel petcock on the right side to turn the fuel off when changing filter, have you verified that petcock is open, could also be worn and sucking air where you turn the petcock.

And yes, the 743 had a manual cable pull shut off, have you verified that the cable is pushing the fuel shutoff lever fully to the run position?

Also, at any point when your at the engine compartment with engine running, and it's laboring to run, does it ever suck the primer bulb flat?
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Customer reply replied 8 years ago

Checked the fuel shut off, it is full on, engine is laboring and missing all the time, but really bad when warmed up, primer bulb is not flat, but the rubber is some what hard from age. I close the fuel return needle on the fuel inlet and it will stay running, missing and laboring, if I open the valve it dies at any throttle position. Going to check fuel think pickup and fuel lines to motor for leaks or restrictions, what is the likely hood of a bad injection pump?


 

Mechanic: Fieldtech59, Shop manager replied 8 years ago
Are we sure we don't have some water in the fuel? Just a thought.

Just for testing purposes let's try something else. Get a clean container of fuel, drop a hose from the electric lift pump you installed into the container of fuel, see how the engine acts then. If it runs proper, connect the hose to the mechanical pump on the engine and see how it runs. By doing this, we're basically going from a known clean container of fuel (temporary tank) to a lift pump (tying both electric and mechanical pump) and then to the injection pump. This will give us a little more info on where to go. Let me know what it does.
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Customer reply replied 8 years ago

Sounds good, Ill let you know the out come, good or bad tomorrow.

Mechanic: Fieldtech59, Shop manager replied 8 years ago
Excellent, I'll be awaiting the news.
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Customer reply replied 8 years ago

Sorry for the wait, found out that my helper (a.k.a. my 80 year old dad) put some fuel in it, upon testing some in a clear bowl found gasoline/ diesel mix, drained entire fuel system and replaced filters funs fine now. Thanks for your help and making my brain change gears.

Mechanic: Fieldtech59, Shop manager replied 8 years ago
Excellent news indeed! This kind of stuff has happened to me before, go through the normal procedures, keep coming up with nothing, have to make yourself get off that rabbit trail and come at it from a different direction and perspective. Good to hear that all is well again. Cheers!
Fieldtech59
Fieldtech59, Shop manager
Category: Construction and Road Equipment
Satisfied Customers: 202
Experience: Construction equipment repair technician since 1986, JLG certified, Shop manager since 2006.
Verified
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Category: Construction and Road Equipment
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