No start 743b

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rcrail

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Sep 28, 2023
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Hey guys, I have a I believe a 99 743b with the 4 cylinder kubota diesel. I initially had problems with the starter relay and thanks to you guys I have that repaired. But now it'll crank but no start. If I cycle the glow plugs it acts like it wants to but just won't fire off. With no glow plugs it doesn't even want to at all. I had it running the other night with a lot of cranking and cycling of glow plugs. I let it run for about 15 minutes and it ran great. Next day, no start. I replaced the lift pump and checked and replaced some hoses, tried to bleed the system but not sure of the complete process. It acts like it not getting fuel. It is puffing a little smoke while cranking. It's not cold enough to even need glow plugs, it should just fire off. So…. What is the process to bleed the air from the fuel system and how can I check to see if I'm getting fuel from the tank?? I hear alot about problems with the pick up tube but since I did have it running the other night I wouldn't think that would be an issue, any random thoughts are welcome as well.
 

laurencen

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Oct 3, 2016
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you have a priming bulb? on the fuel rails by injectors there is a round bleed knob, open it and pump fuel, after a few pumps fuel will be coming out this knob area. sounds like fuel, is the fuel shutoff working
 
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rcrail

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Sep 28, 2023
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you have a priming bulb? on the fuel rails by injectors there is a round bleed knob, open it and pump fuel, after a few pumps fuel will be coming out this knob area. sounds like fuel, is the fuel shutoff working
Yes I do have a priming bulb, I loosened the bleed knob and pumped the bulb. No fuel coming out of the bleeding knob, it has a hose running up to the injectors from the bleeding knob. The primer bulb is tight. Yes the fuel shut off is working in conjunction with the key.
 

brdgbldr

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I have attached a photo of the process for removing air from the fuel system.
 

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rcrail

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I tried bleeding the fuel system, my fuel filter is a little different set up that what's pictured. There is a screw on the front of the fuel filter, I took it out and pumped the primer bulb until I got fresh clear fuel out, put the bolt back in. Opened the bleed knob on the engine that sits just after the low pressure pump and cranked engine, there was no start. If I cycle the glow plugs it acts like it wants to start but won't. It does puff some smoke out the exhaust but not a lot. The machine ran strong prior to sitting for a month, doesn't seem to be any blow by coming from vent tube. I think I've been into a little bit of everything in my life and never ran into anything I can't fix but this diesel is kicking me all around the shop. Right now I'm all over the place mentally, is it getting no fuel or is the engine shot? Any suggestion where to start are appreciated.
 

laurencen

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your 743 is it a electric solenoid or cable to activate fuel shut off, sounds like no fuel to me, the high pressure line to the injector, can you loosen it say 1 turn then crank the motor and see if fuel is getting to the injectors
 

Markle

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Sep 8, 2020
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Just some thoughts based on your description of the issues…if it's puffing some "smoke" when trying to start, that's usually unburnt diesel…my 743, even when weather is warm requires at least 60 seconds of glow before cranking...these kubotas need a lot of glow time. Verify glow plugs are heating by removing each and testing with 12v from a battery. So if you have fuel to injectors, adequate glow heat and time, and if it still hard start, I'd be doing compression test of each cylinder.
 

Tazza

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Another thing you can try is to give it a little ether when cracking, see if that will get her to fire up.

On my old V1702 machines, they always needed glowing, even on warm days. Once warm, it would run all day.

The ones we rebuild, after we set top clearance, the compression alone will get them running, even in the middle of winter we rarely use glow plugs to start them when doing test runs.
 

laurencen

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never use either on the Kubota motor, its the path to a cracked head, the 2 743s I have rebuilt both used either and both had cracked heads

check glow plugs, you can remove them, supply power they should glow quickly on the ends, we use at least 30 to 45 seconds of glow before starting even when temp is +15C
 

oiu789

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Disconnect the jumpers between the glow plugs, set multi meter to the lowest ohm setting, touch one lead to ground and touch other to top of glow plug should see around .8 ohms on each you could check what a new one ohms to compare. This way you do not need to remove the plugs unless they show bad. Does the primer bulb get firm after squeezing and not go soft right away it should stay firm for awhile this indicates that air is not getting back in.
 

Tazza

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never use either on the Kubota motor, its the path to a cracked head, the 2 743s I have rebuilt both used either and both had cracked heads

check glow plugs, you can remove them, supply power they should glow quickly on the ends, we use at least 30 to 45 seconds of glow before starting even when temp is +15C
I have voiced concerns due to hearing ether will cause damage to the boss, he said that it will not cause issues, a piston would fail before a head using ether. These heads crack from being over heated, i'd suspect low compression and they used ether to get them running, possibly making the head gasket fail and causing it to over heat and crack.

With the amount of diesels we rebuild every year, i trust the boss man's advise, as he has been doing this for a very long time.
 
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rcrail

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Sep 28, 2023
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It's definitely not getting fuel, I cracked an injector line and nothing. Replaced the low pressure pump, tested it manually before putting it on, it works good by hand. I pulled a vacuum on the fuel line to get fuel to the low pressure pump. Still would not start. Cycled glow plugs, after that it wanted to start but wouldn't. I gave it a small shot of starting fluid and it fired off and ran fine, and restarted fine. Went out 3 hours later and no start with and without glow plugs. A very short burst of starting fluid and it fired off and ran fine. I find it hard to believe it's wore out, this machine has 1900 hours on it. But anything is possible. I'm testing and replacing glow plugs today because I don't want to have to use starting fluid every time I need it and risk some happening.
I would think it should start without cycling glow plugs on a 60 degree day but definitely with glow plugs cycled it should start. I'm also checking today to make sure it's holding fuel prime today. I've read each response carefully and taken them into account that these machines are notoriously hard to start without glow plugs.
 

haymaker

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Mar 14, 2023
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You did check the fuel line that draws fuel out of the tank and the screen for blockage, right?
 

laurencen

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this has a mechanical pump on side of the motor, the pump is shot, put a electric pump and bypass the mechanical one to try,
 
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laurencen

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Oct 3, 2016
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my guess is fuel pump is weak, cranking pumps next to nothing use either(will destroy motor) and rpm is fast pump does pump some fuel till rpm drops.

install a electric pump to confirm the pump is not working,
 

Gbannish

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Mar 14, 2010
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My 743 became harder and harder to start. I lived with it for at least a year, learning to squeeze the fuel bulb a few times right before starting (was always soft after resting), which helped immensely. Then I found a cracked fuel line to the first injector. Once replaced, it started really quickly.
Good luck,
Greg
 

foton

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I am wondering if you have a small crack or hole in a rubber fuel line that is causing you to loose a vacuum and the fuel is running back in the tank, even though there is supposed to have a check valve in the primmer bulb.
 
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rcrail

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Sep 28, 2023
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I have the starting problem fixed. It was the starter relay went bad and the fuel primer bulb was deteriorated. Now I have hydraulic problems after sitting for 2 months. They were working great when parked.
That's on another thread.
Thanks for all your help guys!
 
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