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bobcat 773 down on power/fuel related

willie59

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At this point, from what you've done thus far, I have no idea what's going on, never seen something like this before, thepumpguysc knows far more about injection systems than I. Just throwing out ideas here.
 

James Clark

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Yes at this point the only thing I haven’t done yet is pull the plate the throttle is hooked to and check these springs that are under there I’m not sure I’ll know if there weak or not I suppose they’ll just let the gov. Ideal down (not sure)
 

Delmer

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I also have installed a clear fuel filter in the fuel line in front of the primer bulb.

what kind of filter? I'd remove it for testing purposes, you still have the stock fuel filters in place, right? CAN you keep this running better by pumping the priming bulb when it's stalling?
 

James Clark

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I’ve bypassed the in-line I installed and went straight to a bottle and when it does stall out, you can keep it running by bumping the primer bulb
When this first started to happen I changed the canister filter then it didn’t help so I the put the inline clear filter on to see if anything was coming from the tank, cause I had already drained it out also
 

Delmer

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Sure seems like either the transfer pump isn't working, or it's sucking air between the bulb and the transfer pump. How about remove the primer bulb? and anything else downstream of the transfer pump and run a hose to your fuel jug from there.
 

James Clark

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ok delmer i'll try this as well so i'll run a bottle straight to the lift pump and bypass everything.
does anyone know if there's an after market elec. lift pump that can be put in the loop and do away with the lift pump or wood this just flood the machine.
 

willie59

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You shouldn't need a different lift pump, such as an electric pump, the mechanical lift pump fitted on that engine works flawlessly on tons of Bobcat machines out there. Of course, it's your choice, you could delete the mechanical pump and install an electric pump, figure out "where" to tap it into the ignition circuit to power it, my only point is why, those mechanical pumps do the task day in and day out on those machines with no worries. I know you stated you replaced the lift pump, but possibly it's faulty? It does happen. Again, I'm grasping at straws here, I'm baffled.
 

James Clark

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Ok iv'e looked into the governor and moved the linkage back and forth and at least when its cold it has plenty of tension on the linkage. Just as a follow up to the hole problem as the engine warms up to operating temp then it has trouble maintaining the RPM's at a good throttle speed to operate the machine, it simply put just ramps up and down and at its low point sometimes it catches it self and ramps up or sometimes it just chokes out at low RMP's and dies.
today i went over all the fuel lines and checked for vac. leaks, which i found none as i loosend some of the hoses i could here the lines sucking in air so the vac. on all the lines seam to be fine and not sucking air.
 

rmllarue91

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Is this and engine that could be affected if return line is plugged ? I've seen worn injection pumps / governor's drop say 500 rpm but never stall this sounds like fuel starvation or intake is restricted. What color smoke when it dies?
 

James Clark

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I've had everything apart but the injectors and the main injector pump and the smoke is perfect, it shows no signs of blow by or anything major.
My question is it runs fine till its warmed up then it stalls and has no power, even dying at points.
Is it possible for a set of injectors to work good when cold then go to hell after the motor has run for 5/10 min.s
Then if not does this theory apply to the injector pump (could it be fine one min then go south after warming up)

Then also would these issues be fine again once the unit is cooled back of then return as it warms up again. I'm just not an expert on the injectors or the pump.
Thx for any input
 

Delmer

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They put those Kubotas in Carrier refer trailer units, they go 20,000+ hours. Usually never get rebuilt, get a new trailer at that point.

Rmllarue asked about smoke, is there black smoke? or at least visible smoke when the engine is warm and surging? If there is, then the engine is getting fuel, if there is not visible smoke, the engine runs when it gets fuel and slows when it's not getting fuel.

That's a simple and reliable inline injection pump, I don't know of anything that would cause this inside the pump. It's a mechanical governor as far as I know, so highly unlikely to break in a way that acts up when warm. An injector that's leaking back combustion into the return could do this, but that's unlikely in my guesstimation.

You know that pumping the priming bulb will keep it running, you could try an electric pump to see what that does, but you already know that the priming bulb will do that. It almost has to be a suction air leak, or a weak transfer pump, or a blockage somewhere. Rubber hoses will often work cold and then leak when warm. Maybe an o ring is doing the same thing?

Before even thinking of touching the injection pump or injectors, put a pressure gauge on the fuel inlet to the injection pump, or close to there, and see what the pressure does from cold to warm.
 

willie59

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I'm scratching my head and thinking the same as you Delmer. Injectors go bad, but not all of them at once, warm or cold. Same with injection pumps, I've never seen anything that makes one flip out when warmed up. Don't mean it can't happen, just never seen it. I agree, stick a new fuel hose on that supply fitting to the injection pump, hook an electric pump on that hose, then another new hose from the electric pump to a clean fuel container. See how it does then cold to warm. If it doesn't falter, then you have something wrong with the supply system of your machine. That's the way I see it.
 

ThreeCW

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James,
Any chance that your primer bulb is collapsed or partially collapsed after you have stalled out?
In the video links below, this fellow had a Bobcat 853 with a fuel starvation problem, with his engine starving out, losing power and stalling after getting warm. When he did prime it before stalling, it ran for 5 minutes and then stalled out again when warm. Sound familiar?
In his case, it turned out to be a restriction in the fuel pickup from the tank ... sounds like it was a fuel strainer / check valve that was plugged (or restricted) with rust or debris. He ended up blowing the plugged strainer / check valve off into the tank using compressed air and installing an in-line fuel filter, in-line check valve and an electric fuel pump to get it running again.
Have a look at Video 4 first to see the result and then the first 3 videos for some of the details.
Even if this is not your problem, his videos might give you some more ideas to troubleshoot your problem further.
Regards, 3CW
Video 4:
Video 1:
Video 2:
Video 3:
 
Last edited:

thepumpguysc

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I was going to suggest a bad primer buld the other day but got side tracked.. sorry bout that..
They're easy to spot in most cases..
IF your going to use an electric pump, get 1 w/ NO MORE than 10 psi.. or you'll flood the pump & it will leak fuel into the crank case..
 

James Clark

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thx threecw i'm at work now but when i get home ill try some of these ideas.
cant tell all of you haw much it means to have some people willing to offer suggestions to solve this issues so thx again
 

James Clark

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Here's a follow up to installing a gauge on the fuel line.
I installed a 0-15 psig gauge right in front of the injector pump, So when i started the 773 it was drawing between 3.5-4.0 psig of fuel into the pump.
after it warmed up, some 5 min or so at 56f temp out doors, it started to stall and loose hp. at that point, and the gauge was down to roughly 3 psig or less. I wish it was liquid filled gauge but its not so it does bounce around a little.
So it did appear to be down a little on flow, so I have a brand new pick up tube ect. for the tank and am going to install it and see what happens then.
Does anyone know what the minimal psig to the injector pump must be to operate the machine properly.

And as usual I can't tell all the people who have been offering suggestions to solve my problem how much I appreciate all of your help
thx again.
 
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