Kawasaki FS730V - new mower - engine issues...

JamesBoyd

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Jun 22, 2020
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1
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Hey Folks!



New member Jim here from SC.


Looking for some advice and help here.


We just bought a place with a 4 acre yard and as such needed a new lawnmower.


We purchased a Kubota Z421 with Kawasaki FS730V. Unit is new and not used.


Unit runs fine at low power demand (less than ¾ throttle and not tall grass) but when run at WOT and/or tall grass – it will run fine for 2-3 mins and then will start to sputter and die… if you disengage the blades and bring it back to ½ throttle, it will surge for a few moments and then smooth out. You can wait for a minute or so and then go back to WOT and start cutting again – and the process repeats itself.


When it just starts to misbehave, if you come all the way off of the throttle, the engine will die. By the time you choke it and turn the key to start, it sits and idles just fine.


I noticed also that the problem seems to be worse if the unit is on an incline.


The Kubota dealers have been little to no help. They report a 2-4 week delay before they can look at the unit and then possible parts delays after that.


Here is what I have done so far:


Removed fuel line from inside the tank to the fuel pump, it is clear and open – no debris in tank, shut off valve is open and lines are clear.
Removed supply line from carb and started the engine – the fuel coming out of pump and headed to carb is flowing well
Added aux tank, ¼” barb, in line fuel filter up above engine (just as a test apparatus) and gravity fed the engine with fuel – problem remained the same
Tested the carb solenoid – appears to be working properly
Removed the main jet, it is not restricted at all
Removed needle and seat, no debris, fuel flows through easily




I do not THINK the problem is electric but don’t want to overlook anything.


The fact that the engine runs fine (even at WOT) for a while – and then when it starts to run poorly - and if the heavy load is removed – the engine will then again start to run fine – makes me think the float bowl is not staying full enough. Also, on an incline, the fuel may come “off” of the main jet a little sooner?


Problem with the float is that it is plastic and does not appear to be adjustable like a metal unit. Float is not fuel logged by the way.


Not sure if the float is “adjustable” in any way?


OK EXPERTS, that is my tale – please help with input if you can?


Yes, I know I should not be working on the unit – but I bought it to cut grass and cannot stomach it sitting at the dealer for 4-6 weeks… and who knows if they will even fix it correctly.


I would even purchase a new carb if I was pretty sure that was the issue – looks like the Kawa replacement is about $250 (would not use an aftermarket). Advice on where to get parts quickly and reasonably priced would be great!


Also I purchased the unit about 150 miles from home, trying not to have to go back to the dealer I bought it from and they would likely tell me the same thing – leave it with us and we will fix it.




Many many thanks!
 

mechanic mark

Lawn Pro
Joined
Jul 15, 2013
Threads
155
Messages
5,745
Hey Folks!



New member Jim here from SC.


Looking for some advice and help here.


We just bought a place with a 4 acre yard and as such needed a new lawnmower.


We purchased a Kubota Z421 with Kawasaki FS730V. Unit is new and not used.


Unit runs fine at low power demand (less than ¾ throttle and not tall grass) but when run at WOT and/or tall grass – it will run fine for 2-3 mins and then will start to sputter and die… if you disengage the blades and bring it back to ½ throttle, it will surge for a few moments and then smooth out. You can wait for a minute or so and then go back to WOT and start cutting again – and the process repeats itself.


When it just starts to misbehave, if you come all the way off of the throttle, the engine will die. By the time you choke it and turn the key to start, it sits and idles just fine.


I noticed also that the problem seems to be worse if the unit is on an incline.


The Kubota dealers have been little to no help. They report a 2-4 week delay before they can look at the unit and then possible parts delays after that.


Here is what I have done so far:


Removed fuel line from inside the tank to the fuel pump, it is clear and open – no debris in tank, shut off valve is open and lines are clear.
Removed supply line from carb and started the engine – the fuel coming out of pump and headed to carb is flowing well
Added aux tank, ¼” barb, in line fuel filter up above engine (just as a test apparatus) and gravity fed the engine with fuel – problem remained the same
Tested the carb solenoid – appears to be working properly
Removed the main jet, it is not restricted at all
Removed needle and seat, no debris, fuel flows through easily




I do not THINK the problem is electric but don’t want to overlook anything.


The fact that the engine runs fine (even at WOT) for a while – and then when it starts to run poorly - and if the heavy load is removed – the engine will then again start to run fine – makes me think the float bowl is not staying full enough. Also, on an incline, the fuel may come “off” of the main jet a little sooner?


Problem with the float is that it is plastic and does not appear to be adjustable like a metal unit. Float is not fuel logged by the way.


Not sure if the float is “adjustable” in any way?


OK EXPERTS, that is my tale – please help with input if you can?


Yes, I know I should not be working on the unit – but I bought it to cut grass and cannot stomach it sitting at the dealer for 4-6 weeks… and who knows if they will even fix it correctly.


I would even purchase a new carb if I was pretty sure that was the issue – looks like the Kawa replacement is about $250 (would not use an aftermarket). Advice on where to get parts quickly and reasonably priced would be great!


Also I purchased the unit about 150 miles from home, trying not to have to go back to the dealer I bought it from and they would likely tell me the same thing – leave it with us and we will fix it.




Many many thanks!
First & foremost do not mess with it, if they find out, they may void warranty. Next & most important, always use 93 octane gasoline with a quality brand fuel additive.
Hey Folks!



New member Jim here from SC.


Looking for some advice and help here.


We just bought a place with a 4 acre yard and as such needed a new lawnmower.


We purchased a Kubota Z421 with Kawasaki FS730V. Unit is new and not used.


Unit runs fine at low power demand (less than ¾ throttle and not tall grass) but when run at WOT and/or tall grass – it will run fine for 2-3 mins and then will start to sputter and die… if you disengage the blades and bring it back to ½ throttle, it will surge for a few moments and then smooth out. You can wait for a minute or so and then go back to WOT and start cutting again – and the process repeats itself.


When it just starts to misbehave, if you come all the way off of the throttle, the engine will die. By the time you choke it and turn the key to start, it sits and idles just fine.


I noticed also that the problem seems to be worse if the unit is on an incline.


The Kubota dealers have been little to no help. They report a 2-4 week delay before they can look at the unit and then possible parts delays after that.


Here is what I have done so far:


Removed fuel line from inside the tank to the fuel pump, it is clear and open – no debris in tank, shut off valve is open and lines are clear.
Removed supply line from carb and started the engine – the fuel coming out of pump and headed to carb is flowing well
Added aux tank, ¼” barb, in line fuel filter up above engine (just as a test apparatus) and gravity fed the engine with fuel – problem remained the same
Tested the carb solenoid – appears to be working properly
Removed the main jet, it is not restricted at all
Removed needle and seat, no debris, fuel flows through easily




I do not THINK the problem is electric but don’t want to overlook anything.


The fact that the engine runs fine (even at WOT) for a while – and then when it starts to run poorly - and if the heavy load is removed – the engine will then again start to run fine – makes me think the float bowl is not staying full enough. Also, on an incline, the fuel may come “off” of the main jet a little sooner?


Problem with the float is that it is plastic and does not appear to be adjustable like a metal unit. Float is not fuel logged by the way.


Not sure if the float is “adjustable” in any way?


OK EXPERTS, that is my tale – please help with input if you can?


Yes, I know I should not be working on the unit – but I bought it to cut grass and cannot stomach it sitting at the dealer for 4-6 weeks… and who knows if they will even fix it correctly.


I would even purchase a new carb if I was pretty sure that was the issue – looks like the Kawa replacement is about $250 (would not use an aftermarket). Advice on where to get parts quickly and reasonably priced would be great!


Also I purchased the unit about 150 miles from home, trying not to have to go back to the dealer I bought it from and they would likely tell me the same thing – leave it with us and we will fix it.




Many many thanks!
First & foremost do not mess with engine,etc, may void warranty. Always use 93 octane gasoline with a quality brand fuel treatment. https://www.lawnmowerforum.com/threads/john-deere-fuel-treatment.56774/#post-343220 Let us know how it goes, thanks, Mark https://www.google.com/search?q=startron+fuel+treatment&oq=STARTRON&aqs=chrome.1.69i57j35i39j0l6.9732j0j7&sourceid=chrome&ie=UTF-8
 
Last edited:

tom3

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Joined
Apr 9, 2018
Threads
25
Messages
1,577
Two things I see, internally vented carb, and symptoms of fuel starvation. But I'd get in touch with the dealer, or a rep. from Kubota, and get the mower in the shop and take home a loaner.
 

cpurvis

Lawn Addict
Joined
Aug 25, 2015
Threads
18
Messages
2,053
I'm with Tom--let Kubota fix it. Also agree with his diagnosis--fuel starvation.
 

mechanic mark

Lawn Pro
Joined
Jul 15, 2013
Threads
155
Messages
5,745
I would return mower & purchase one of their diesel engine models, you'll be glad you did. My nephews dad has at least a dozen Kubota Diesels they use to mow all their properties & have been doing so for at least 20 years. They will not even talk about anything but Kubota mowers with Kubota Diesel Engines. The Japanese make a top quality product in Kubota Diesels.
 
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