motor bogs then stall under full load?

[743bobcat]

new to this forum so if this is answered somewhere else please direct me. I have an older (believe 80's) 743 bobcat with a kubota diesel. Since I have owned it about (7-8 yrs) I am unable to run it under full load. By that I mean half stick forward or reverse, going up hills slows to a stall. At first I lived with it now it is frustrating as it will randomly stall now. I have replaced many parts over the years but am willing to start over incase I missed something obvious. any ideas? thanks in advance

 

[Tazza]

Start with a new air filter, inner and outer.
The other issues could be fuel filter is blocked, the bleeding valve on the injector pump fuel inlet could be slightly open giving lower fuel pressure to the pump. Injectors could be dirty, lift pump could be sad. Start with the simple things first.

 

[Tazza]

Start with a new air filter, inner and outer.
The other issues could be fuel filter is blocked, the bleeding valve on the injector pump fuel inlet could be slightly open giving lower fuel pressure to the pump. Injectors could be dirty, lift pump could be sad. Start with the simple things first.

One i forgot about is a blocked pickup tube/screen or junk stuck in the elbow. If you get a bottoe of fresh fuel and tie it inside the engine bay and run the engine from that, it eliminates the tank and pickup tube, see if it makes any difference.

 

[743bobcat]

One i forgot about is a blocked pickup tube/screen or junk stuck in the elbow. If you get a bottoe of fresh fuel and tie it inside the engine bay and run the engine from that, it eliminates the tank and pickup tube, see if it makes any difference.

going to start by running with no airfilter. I appreciate the insite. I didn't want to taint your info by listing all I have replaced in the last few years. but for some reason I was stuck on a fuel issue. Its pouring here so I haven't tried air filter yet. but I have replaced complete fuel line (started cause fuel line in tank fell apart) so new screen, pick up tube,elbow, all lines, cleaned tank while I had it out, fuel filter(bobcat part), the only part (which was my next step) was the pump bowl incase it was coming apart inside.

 

[mrfixitpaul]

going to start by running with no airfilter. I appreciate the insite. I didn't want to taint your info by listing all I have replaced in the last few years. but for some reason I was stuck on a fuel issue. Its pouring here so I haven't tried air filter yet. but I have replaced complete fuel line (started cause fuel line in tank fell apart) so new screen, pick up tube,elbow, all lines, cleaned tank while I had it out, fuel filter(bobcat part), the only part (which was my next step) was the pump bowl incase it was coming apart inside.

another thing to check....make sure that the engine stop lever moves fully against it's tab when you push the cable down.

 

[743bobcat]

another thing to check....make sure that the engine stop lever moves fully against it's tab when you push the cable down.

thanks will check. did look at that before cable seems to wander when pushing.(kind of feels like it has spring)had a dynahoe where the emergency stop was quirky. but this one is driving me crazy!!!!

 

[Tazza]

thanks will check. did look at that before cable seems to wander when pushing.(kind of feels like it has spring)had a dynahoe where the emergency stop was quirky. but this one is driving me crazy!!!!

Another one to check with the fuel delivery. Run the machine, get someone to squeeze the primer bulb when you try and rev it, see if it speeds up when given more pressure.

 

[743bobcat]

Another one to check with the fuel delivery. Run the machine, get someone to squeeze the primer bulb when you try and rev it, see if it speeds up when given more pressure.

tried running without airfilter seemed to be better but still not right. filter didn't look to bad but I will replace both anyway. seemed to be fine on flat ground but up hill gradually stalled again. half stick is still fine. forgot to mention before that when I go back down the hill it revs up high. thanks for the input. will continue to try all of these

 

[743bobcat]

tried running without airfilter seemed to be better but still not right. filter didn't look to bad but I will replace both anyway. seemed to be fine on flat ground but up hill gradually stalled again. half stick is still fine. forgot to mention before that when I go back down the hill it revs up high. thanks for the input. will continue to try all of these

also you mention the beelding valve, it is closed. but what about the return lines on the injectors? mine look at little brittle could that cause an air leak? thanks again

 

[Tazza]

also you mention the beelding valve, it is closed. but what about the return lines on the injectors? mine look at little brittle could that cause an air leak? thanks again

It could cause an air leak, but they are tap off lines, they will not cause air to get into the inlet of the injector pump. The fuel just pours back into the fuel tank and is picked up by the pickup tube.
As you said slopes make the throttle change, something soulds like it could be loose. Do you get any smoke at full throttle?
I wonder if there is an issue with the spring for the govenor. If you remove the throttle linkage, then remove the plate that the arm come out of from the engine. You may also need to remove the stop lever plate too, i'm not sure. There should be two springs that connect from the throttle lever to the govenor arm inside the engine. Does any of that make sense? If there is a problem with the springs, it will not put enough tension on the govenor and it simply will not throttle up.

 

[743bobcat]

It could cause an air leak, but they are tap off lines, they will not cause air to get into the inlet of the injector pump. The fuel just pours back into the fuel tank and is picked up by the pickup tube.
As you said slopes make the throttle change, something soulds like it could be loose. Do you get any smoke at full throttle?
I wonder if there is an issue with the spring for the govenor. If you remove the throttle linkage, then remove the plate that the arm come out of from the engine. You may also need to remove the stop lever plate too, i'm not sure. There should be two springs that connect from the throttle lever to the govenor arm inside the engine. Does any of that make sense? If there is a problem with the springs, it will not put enough tension on the govenor and it simply will not throttle up.

I pulled both covers off. its hard to see but looks like both springs are there and in tact. hard to tell but looks like they move on a lever behind the engine stop plate. Like it has a slider? I didn't try to take them out. Ran out of time today but will get to it tomorrow. I was hoping to find a broken spring and an easy fix. but nothing obvious although it looks like someone has been in here before. the more I think about it it really isn't a "bog". Its more like there is no govenor working like if you tried to drive a truck with a creeper gear up a hill without using the throttle. I know I've said this before but it bears repeating: I really appreciate all the help!!! sometimes it just takes a second set of eyes. I'll see if I can get the spring out tomorrow maybe the inside is broken? thanks

 

[Tazza]

I pulled both covers off. its hard to see but looks like both springs are there and in tact. hard to tell but looks like they move on a lever behind the engine stop plate. Like it has a slider? I didn't try to take them out. Ran out of time today but will get to it tomorrow. I was hoping to find a broken spring and an easy fix. but nothing obvious although it looks like someone has been in here before. the more I think about it it really isn't a "bog". Its more like there is no govenor working like if you tried to drive a truck with a creeper gear up a hill without using the throttle. I know I've said this before but it bears repeating: I really appreciate all the help!!! sometimes it just takes a second set of eyes. I'll see if I can get the spring out tomorrow maybe the inside is broken? thanks

If the springs are still there its not broken... Thats correct with what you describe. The govenor is behind the allow housing, it uses steel balls that get flung out causing resistance, thats what that arm is. The other end goes to the injector pump to adjust the fuel delivery to the injectors.
I'm really not sure where to go from here. The govenor runs in oil, so it shouldn't be locked up, but its always possible i guess. It could be a pump issue too.... So many possibilities.

 

[743bobcat]

If the springs are still there its not broken... Thats correct with what you describe. The govenor is behind the allow housing, it uses steel balls that get flung out causing resistance, thats what that arm is. The other end goes to the injector pump to adjust the fuel delivery to the injectors.
I'm really not sure where to go from here. The govenor runs in oil, so it shouldn't be locked up, but its always possible i guess. It could be a pump issue too.... So many possibilities.

I know this thread is old but had alot going on in the last couple years. still having the same problem with my 743 stalling under full throttle. was using it yesterday and I'm wondering if it has to do with replenishing valves? first was thinking that maybe auxilliary hydraulics were bleeding through (found linkage not connected) but now I see that it is a seperate system. I'm begining to think that it could be too much pressure? as always I appreciate the help

 

[Tazza]

I know this thread is old but had alot going on in the last couple years. still having the same problem with my 743 stalling under full throttle. was using it yesterday and I'm wondering if it has to do with replenishing valves? first was thinking that maybe auxilliary hydraulics were bleeding through (found linkage not connected) but now I see that it is a seperate system. I'm begining to think that it could be too much pressure? as always I appreciate the help

Does it start ok? Will it stall when idling? any black smoke at idle like its straining to run? if not, i don't believe your aux is stuck on.
At a decent throttle the hydraulic system will not stall your machine, the drive system has enough load to be able to stall it though.
I can't see the replenishing valves would do it, they only supply fresh oil to the pump, not creating more of a load. I still think its an engine issue pulling it down.... If you have a good fresh supply of fuel and no air restrictions, good compression the engine should be good. But you would need to test it.

 

[743bobcat]

Does it start ok? Will it stall when idling? any black smoke at idle like its straining to run? if not, i don't believe your aux is stuck on.
At a decent throttle the hydraulic system will not stall your machine, the drive system has enough load to be able to stall it though.
I can't see the replenishing valves would do it, they only supply fresh oil to the pump, not creating more of a load. I still think its an engine issue pulling it down.... If you have a good fresh supply of fuel and no air restrictions, good compression the engine should be good. But you would need to test it.

i havent tested compression I'll try to get to that here is what I noticed so far: no smoke before or when it stalls (not noticable anyway I'm in the cab) no smoke on restart and restart is easy stalling is no different hot or cold I have owned for ten ish yrs and has never got worse or better any full throttle zero turn will stall ( half throttle will turn ok) on level ground full throttle is ok going down hill engine will rev regardless of throttle position (however machine does not speed up almost like an engine brake) going up a hill the steeper the faster it will stall, I have learned early on to work the throttle to avoid stalling. I don't think that I have ever stalled using the bucket hydaulics If I dig into a pile of material at anything above about half stick it will stall if I leave the machine idleing with no brake it will creep In looking at the flow chart for the drive system I saw "switches" and "valves" an started to wonder if maybe I'm "locking" the system somehow. if a valve isn't opening to bleed off extra? thanks

 

[mrdeere1959]

i havent tested compression I'll try to get to that here is what I noticed so far: no smoke before or when it stalls (not noticable anyway I'm in the cab) no smoke on restart and restart is easy stalling is no different hot or cold I have owned for ten ish yrs and has never got worse or better any full throttle zero turn will stall ( half throttle will turn ok) on level ground full throttle is ok going down hill engine will rev regardless of throttle position (however machine does not speed up almost like an engine brake) going up a hill the steeper the faster it will stall, I have learned early on to work the throttle to avoid stalling. I don't think that I have ever stalled using the bucket hydaulics If I dig into a pile of material at anything above about half stick it will stall if I leave the machine idleing with no brake it will creep In looking at the flow chart for the drive system I saw "switches" and "valves" an started to wonder if maybe I'm "locking" the system somehow. if a valve isn't opening to bleed off extra? thanks

could be timing? never know. if its been that way as long as you have had it maybe someone has worked on it before and timing is not right

 

[743bobcat]

could be timing? never know. if its been that way as long as you have had it maybe someone has worked on it before and timing is not right

its diesel so no timing per se. I don't have a pressure guage that reads 1400psi so can't check pump pressure but will try to check pump timing. probably should have used a different word. really not a "bog" more of a stall. thats why I thought it was fuel from beginning but not much left in fuel system to replace. thanks for the input.

 

[mrdeere1959]

its diesel so no timing per se. I don't have a pressure guage that reads 1400psi so can't check pump pressure but will try to check pump timing. probably should have used a different word. really not a "bog" more of a stall. thats why I thought it was fuel from beginning but not much left in fuel system to replace. thanks for the input.

The injector pump is timed. If its not right you can have a lack of power.

 

[7LBSSMALLIE]

The injector pump is timed. If its not right you can have a lack of power.

you mentioned playing with throttle. are you running at full, as unit was designed to do. you might not have an issue.