Bobcat 743 - Starts then dies

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Joined
May 9, 2023
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Hi. all, starting a new thread since I figured out the other issue.

Still on a quest to get my uncle's Bobcat 743 serial #5019-M-301-39 with the Kubota V1702. When I moved it to my property, the problem was that it would run for anywhere between 1-10 minutes but would die on its own or under load at times. It very much seemed like a fuel delivery issue. Bleeder valve was found open, primer bulb would not prime, unknown when the last time the pickup tube and fuel filter were replaced. Earlier this week it stopped firing up all together after adding some fuel.

Steps I have taken so far:
Removed fuel tank, emptied, cleaned out of all junk(there was a lot) replaced the pickup tube with the one way filter and reinstalled.
Cleaned all the fuel lines with compressed air and reinstalled. Did not replace.
Replaced the fuel filter with a Wix filter
Replaced the primer bulb
Primed the system with the bulb to the filter valve
Primed the system with the bulb to the bleeder valve on the pump

I got it to fire up again but still dies shortly after. The bulb was not firm but was also not flat which tells me fuel is flowing now with no clogs along the way now. If I prime it again, it will fire a little, sputter and die, or run for a minute and die. I have a lift pump, glow plugs, and injectors coming in today and tomorrow just in case, but is there anything else I should look at or do before any of these other things? Am I on the right track?

I would appreciate any feedback on any potential easy wins here.
 

foton

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Mar 1, 2018
Messages
1,277
I believe that you are on the right track, I also think your kubota would continue to run once the air is worked out completely , but since you have all those parts coming in you might as well wait and replace all the parts then prime everything up as best as you can and then go down the restart mode. make sure that the main fuel filter is full of diesel it takes a lot of turning over just to fill it so fill it first before installing.
 

Cary E Sip Sr

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Joined
Jan 16, 2023
Messages
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I just had similar problem last winter after boys ran it out of fuel . Primer bulbs suck in cold weather , especially when they are mounted where you can't reach them. I believe book said open bleeder on filter first and prime. I gave up on bulb and used air hose in tank to get good fuel volume at filter . Close filter bleeder , open bleeder on injector pump., prime again and start. After running good , then close injector bleeder. At that point mine ran fine , if not , I may have proceeded to crack injector lines but didn't have too. If fuel is flowing to both bleeders , but not injectors , I would suspect injector pump trouble . Eliminate the simple things first ,( like screens on suction tubes , my pet peeve ) , by the time you get to injector pump problems you're talking $ .
 

Cary E Sip Sr

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Joined
Jan 16, 2023
Messages
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Oh , I was taught it's either spark or gas . Gas was covered , I'd like to add one thing I've found on the spark problem . Use a test light grounded to a good bolt or right to the battery. Test the +coil wire going into the distributor. If it test lights up on the hot side of the points , but no spark when spinning motor , it maybe the body of the points are not grounding to the distributor like your test light is to the battery. A couple of reasons maybe
corrosion under points body & mounting screws, or rust proofing shellac spray at manufacturing . Clean and lightly scratch or sand , and spray with some rust proofer like wd40 . Now check for spark.
 

cdmccul

Well-known member
Joined
Jun 18, 2013
Messages
504
Oh , I was taught it's either spark or gas . Gas was covered , I'd like to add one thing I've found on the spark problem . Use a test light grounded to a good bolt or right to the battery. Test the +coil wire going into the distributor. If it test lights up on the hot side of the points , but no spark when spinning motor , it maybe the body of the points are not grounding to the distributor like your test light is to the battery. A couple of reasons maybe
corrosion under points body & mounting screws, or rust proofing shellac spray at manufacturing . Clean and lightly scratch or sand , and spray with some rust proofer like wd40 . Now check for spark.
Good diagnostic advice, but just an fyi, this is a diesel (Model number ends in "3").
 

Tazza

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Dec 7, 2004
Messages
16,829
It could even be an issue with your lift pump, put an electric pump in, instead of the mechanical lift pump.

Pumps generally do not work then stop and work again like that. They generally work or not work. Plungers can get stuck from sitting, but once free, they normally stay that way.
 

Micheal

Active member
Joined
Apr 23, 2023
Messages
26
It could even be an issue with your lift pump, put an electric pump in, instead of the mechanical lift pump.

Pumps generally do not work then stop and work again like that. They generally work or not work. Plungers can get stuck from sitting, but once free, they normally stay that way.
It may be a read valve in lift pump, i bought one on Amazon $52.00
 
OP
OP
J
Joined
May 9, 2023
Messages
5
Hi all, I listened to all your suggestions and kept working at it. Thursday evening I received all the parts I ordered but I wasn't convinced that swapping them all in would cure the problem. I pulled the lift pump to test it. I moved the hose that jumps to the injector pump into the inlet. I tested the pump and was squirting but would pick up air sometimes. I repositioned the hose then it started squirting like I believe it should. I replaced the line and put a clear inline filter to see what was happening. At that point, I could see that now fuel was flowing and air was no longer being trapped. And what do you know, she fired right up and ran better than ever.

Long story short, it had a lot of problems, up to and including the fuel lines themselves being faulty.
Full list of things done/replaced:
Removed fuel tank, emptied, cleaned out of all junk(there was a lot) replaced the pickup tube with the one way filter and reinstalled.
Cleaned all the fuel lines with compressed air and reinstalled. Did not replace.
Replaced the fuel filter with a Wix filter
Replaced the primer bulb
Primed the system with the bulb to the filter valve
Primed the system with the bulb to the bleeder valve on the pump
replaced fuel lines themselves

It has now ran for 10 hours without dying and any issues.
 

foton

Well-known member
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Mar 1, 2018
Messages
1,277
you might not have seen it but i am leaning towards a vacuum leak you fixed and did not know it right away, but good going on getting it runnin.
 
OP
OP
J
Joined
May 9, 2023
Messages
5
you might not have seen it but i am leaning towards a vacuum leak you fixed and did not know it right away, but good going on getting it runnin.
Yes, absolutely. The small jumper hose was definitely introducing air into the fuel system, which was mostly the root of the problem.
 
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