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Discussion Starter · #1 ·
Happy new year to all!
Thank for all the information and support you have provided to so many of us over the years.
I have a very used hustler Super mini Z with a Kawasaki fh680v that kept leaking oil, if it wasn't from the top crankcase seal, then from the bottom and I kept replacing seals every year until last month I found the mower sitting in a pool of oil and I decided to replace it with a used kawasaki fh721V that I bought on ebay as a good running engine that kept blowing head gaskets.
I replaced the head gasket and installed the engine. When I started it, it wanted to rev really hi so I set the governor according to the manual and now the engine throttles perfectly and runs smooth at hi and low revs, but in the process I found that it dies when it warms up.
The best description I can give is that when cold, I can go fast and climb a hill and the engine does not feel it, but after a minute,going forward from a stop will kill it and engaging the blades also. If I choke the engine, it starts right up again.
I have changed the carburetor, the fuel filter, the fuel solenoid, the engine does not smoke nor there is smoke in the dipstick.
I have no idea if the problem is fuel related (my gut feeling) or electrical,but I have read and searched here and in YouTube and have not been able to find a clue as to how to fix the problem.
I am hoping someone can suggest what to do.
Sorry for the long winded post and thanks in advance for reading it.:confused:
 

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Either the coils, or possibly ...

I had a persistent problem on a mower with a V-twin Kawasaki, long story short it turned out one of the plastic pieces that holds the throttle / choke linkage was cracked... In my case it was the choke linkage, the crack made it so the engine would choke fine but it wouldn't unchoke completely and thus as soon as it warmed up I'd lose power.

Specifically the metal rods that connect to the carburetor, when one of these plastic pieces breaks or is cracked it may still be connected but it's no longer operating the way it should... It's worth checking these up close visually, perhaps move the linkages by hand (you may have to operate the choke / throttle lever) to ensure smooth operation.


Machine Gas Engineering Nickel Automotive wheel system
 

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Discussion Starter · #4 ·
Sounds like you might be dropping a coil. Pull one coil wire at a time when it starts acting up. If it dies when one wire is pulled then you know it's the other side that is going bad.
I ordered new coils and will be replacing them today, but if it is the coils, why does it start right up immediatety afterwards?
I almost seems like you turn the key off.
Thanks.
 

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Discussion Starter · #5 ·
Either the coils, or possibly ...

I had a persistent problem on a mower with a V-twin Kawasaki, long story short it turned out one of the plastic pieces that holds the throttle / choke linkage was cracked... In my case it was the choke linkage, the crack made it so the engine would choke fine but it wouldn't unchoke completely and thus as soon as it warmed up I'd lose power.

Specifically the metal rods that connect to the carburetor, when one of these plastic pieces breaks or is cracked it may still be connected but it's no longer operating the way it should... It's worth checking these up close visually, perhaps move the linkages by hand (you may have to operate the choke / throttle lever) to ensure smooth operation.


View attachment 530895
The linkage pieces in my carb are metal and are working fine. The choke does not get stuck and is working fine.
I also replaced the solenoid in the picture.
Thanks.
 

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The best description I can give is that when cold, I can go fast and climb a hill and the engine does not feel it, but after a minute,going forward from a stop will kill it and engaging the blades also.
Sorry for the long winded post and thanks in advance for reading it.:confused:
When you got the engine, was it plug and play or did you have to mess with the wires ?

You did plug the wires back on to the voltage regulator ?

How old is the battery ?

At the battery terminals, do you have 13.6 volts ?

With the engine running at WOT, are you getting 14 + volts ?

The chances of 2 coils going out at the same time are like my chances of winning the Mega Million......
Unless one was already dead, then the other dying.....
Let us know how that works out......

Fuel valve fully open ?

If you are running saddle tanks, there could be trash partially blocking the pickup/valve at the bottom of the tank. The same goes for the valve to switch tanks if you have one.

Hi ho Hi ho............
.
 
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Either the coils, or possibly ...
He put a new carb on it.......Even if he did have the plastic connectors on the original carb, it would not kill the engine......Just make it harder to start.
..
 

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Discussion Starter · #8 ·
When you got the engine, was it plug and play or did you have to mess with the wires ?

You did plug the wires back on to the voltage regulator ?

How old is the battery ?

At the battery terminals, do you have 13.6 volts ?

With the engine running at WOT, are you getting 14 + volts ?

The chances of 2 coils going out at the same time are like my chances of winning the Mega Million......
Unless one was already dead, then the other dying.....
Let us know how that works out......

Fuel valve fully open ?

If you are running saddle tanks, there could be trash partially blocking the pickup/valve at the bottom of the tank. The same goes for the valve to switch tanks if you have one.

Hi ho Hi ho............
.
The Fh721v is the same engine as the fh680v, just a couple of horsepower more and it was plug and play, so the voltage regulator is connected the same as the old one.
The battery is a year old, but it is strong. I have not measured the volts when charging, but that is easy enough to do.
I checked spark and have spark at both cylinders, the engine runs smooth until it dies.
I am using only one of the saddle tanks with no fuel valve, and fuel flows freely from the tank.
Checked the fuel pump and it is pumping.
Thanks.
 

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Discussion Starter · #10 ·
When it dies, you have to verify if it lost spark, or fuel.

My bet is either losing fuel, or something in the OPS system is malfunctioning. The latter is easy to test.
Yes, that is it. How do you verify if it lost spark or fuel when it is not running, and it starts again right away?
Pardon my ignorance. What is OPS?
Thanks
 

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Fuel valve fully open ?

If you are running saddle tanks, there could be trash partially blocking the pickup/valve at the bottom of the tank. The same goes for the valve to switch tanks if you have one.

Hi ho Hi ho............
.
Is the tank venting properly? If it is fuel, like Breezmeister said could be blockage at the bottom of tank....
 

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Yes, that is it. How do you verify if it lost spark or fuel when it is not running, and it starts again right away?
Pardon my ignorance. What is OPS?
Thanks
OPS= Operator Presence System

When it dies, don't try and start it. See if you can get the plug out of the bottom of the carb before restarting. If fuel runs out, it likely isn't running out of fuel, so it must then be losing spark.
Disconnect the engine kill wire from the machine after starting. Go run it. If it still dies, then you have a problem within the engine. If it doesn't it's an OPS problem or a short somewhere within the kill system. Remember, you may need to power the fuel cut off solenoid from another source as it may also be tied into your OPS system. Some are, most are not. Eliminate what it isn't, and you will find what it is.

I'm going to suggest you find a shop to take it to. It doesn't seem you know much about these systems and how they work. You really need a manual for both the engine and the machine with wiring diagrams so you can see how the two systems are tied together. Guessing isn't diagnosing.
 

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He put a new carb on it.......Even if he did have the plastic connectors on the original carb, it would not kill the engine......Just make it harder to start..
Might be the choke linkage closes good, but it doesn't open completely...
Then it will start fine, and as soon as it warms up it loses power.
If a linkage is loose often the choke can be adjusted enough to still close...
But once you get moving the play in the linkage allows for play in the choke valve, and that play allows the plate to close even partially it cuts the air flow and thus power.

The linkage pieces in my carb are metal and are working fine. The choke does not get stuck and is working fine.
I also replaced the solenoid in the picture.
Thanks.
On the metal ones, inside the hole where the linkage hooks to the carburetor there is a hard plastic grommet piece or there should be... That was the problem I had, the little hard plastic grommet inside that hole was cracked and allowing linkage play. It was so minor, took me literally years to track it down.

I did the same as you, both coils, valves, fuel lines and filter, cleaned up underneath the covers real good... I was at wits end. I took it to a repair shop twice and it didn't act up when I was there, not even driving it around and engaging the blades but take it out to mow for a day and I couldn't even finish the first yard.
I replaced gas caps too, thinking if a gas cap vent was clogged.

When I replaced the carburetor...
Which at this stage I was just replacing parts, but it came with the new plastic pieces.
That's when I saw the problem.

Linkages on these things...

Here's the old thread on that FH721V:

It would start awesome, run good for a few minutes and then the nonsense would start...
 

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Might be the choke linkage closes good, but it doesn't open completely...
Then it will start fine, and as soon as it warms up it loses power.
If a linkage is loose often the choke can be adjusted enough to still close...
But once you get moving the play in the linkage allows for play in the choke valve, and that play allows the plate to close even partially it cuts the air flow and thus power.



On the metal ones, inside the hole where the linkage hooks to the carburetor there is a hard plastic grommet piece or there should be... That was the problem I had, the little hard plastic grommet inside that hole was cracked and allowing linkage play. It was so minor, took me literally years to track it down.

I did the same as you, both coils, valves, fuel lines and filter, cleaned up underneath the covers real good... I was at wits end. I took it to a repair shop twice and it didn't act up when I was there, not even driving it around and engaging the blades but take it out to mow for a day and I couldn't even finish the first yard.
I replaced gas caps too, thinking if a gas cap vent was clogged.

When I replaced the carburetor...
Which at this stage I was just replacing parts, but it came with the new plastic pieces.
That's when I saw the problem.

Linkages on these things...

Here's the old thread on that FH721V:

It would start awesome, run good for a few minutes and then the nonsense would start...

And none of that would cause it to die suddenly as if the key was turned off.
 

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Discussion Starter · #16 ·
Might be the choke linkage closes good, but it doesn't open completely...
Then it will start fine, and as soon as it warms up it loses power.
If a linkage is loose often the choke can be adjusted enough to still close...
But once you get moving the play in the linkage allows for play in the choke valve, and that play allows the plate to close even partially it cuts the air flow and thus power.



On the metal ones, inside the hole where the linkage hooks to the carburetor there is a hard plastic grommet piece or there should be... That was the problem I had, the little hard plastic grommet inside that hole was cracked and allowing linkage play. It was so minor, took me literally years to track it down.

I did the same as you, both coils, valves, fuel lines and filter, cleaned up underneath the covers real good... I was at wits end. I took it to a repair shop twice and it didn't act up when I was there, not even driving it around and engaging the blades but take it out to mow for a day and I couldn't even finish the first yard.
I replaced gas caps too, thinking if a gas cap vent was clogged.

When I replaced the carburetor...
Which at this stage I was just replacing parts, but it came with the new plastic pieces.
That's when I saw the problem.

Linkages on these things...

Here's the old thread on that FH721V:

It would start awesome, run good for a few minutes and then the nonsense would start...
If there is one thing I am sure of is that the problem is not the choke. It works perfect, nothing cracked on the linkages. If it was choke related the engine would begin to run rough, but the engine runs smooth, warms up and dies under load.
Thanks.
 

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From a strictly deductive reasoning angle, it sure seems like an electrical issue if it just plain turns off. When it dies, does it sputter dropping RPM until it simply dies, or does it go straight to off like a kill switch?
 

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Discussion Starter · #18 ·
OPS= Operator Presence System

When it dies, don't try and start it. See if you can get the plug out of the bottom of the carb before restarting. If fuel runs out, it likely isn't running out of fuel, so it must then be losing spark.
Disconnect the engine kill wire from the machine after starting. Go run it. If it still dies, then you have a problem within the engine. If it doesn't it's an OPS problem or a short somewhere within the kill system. Remember, you may need to power the fuel cut off solenoid from another source as it may also be tied into your OPS system. Some are, most are not. Eliminate what it isn't, and you will find what it is.

I'm going to suggest you find a shop to take it to. It doesn't seem you know much about these systems and how they work. You really need a manual for both the engine and the machine with wiring diagrams so you can see how the two systems are tied together. Guessing isn't diagnosing.
I will disconnect the engine kill wire and check to see if check if I can find a short in the OPS, those are great suggestions.
For now, I am going to ignore the suggestion to take it to a shop. Not that I haven't thought about it.
BTW I have the service manual for the kawasaki and the mower. They do not have troubleshooting steps that help in my case.
Thanks.
 

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BTW I have the service manual for the kawasaki and the mower. They do not have troubleshooting steps that help in my case.
Thanks.
No I don't imagine that they do. Most books don't. But they do have wiring diagrams, or should. A book doesn't usually tell you how to diagnose a problems, they give you the information you need to be able to fix a problem, or references that help you to diagnose.
 
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