Engine surges and sometimes stalls after running perfectly for 20-30 minutes.

[evanwellens]

Not sure what's going on. I'll get like 1/2 way through my yard and poof the surging starts. If I lower the throttle a sit a few it will come back but not for long.

Here's a video of it in action.

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Model is : Kawasaki FH661V for cub cadet rzt 50. Been a solid champ for years, except this one ;-(
This season , new plugs , fuel filter , oil , oil filter , air filter.
Any ideas on how to troubleshoot ? Was thinking of a carb rebuild or replacement , but the symptoms don't seem to indicate that to me. I shouldn't run so well and then go bad. Happens every time I use it.

 

[Joe Kuhn]

Does it still happen if you loosen the gas cap?

 

[bertsmobile1]

Most likely but not exclusively it could be floating debris in the fuel tank getting sucked into the outlet blocking it off.
Next time it happens pull the fuel line from the item closest to the fuel tank and blowback hard through the tank.
Problem goes away for another 20 minutes or so = trash build up.

Note the fuel pump has a check valve on it so don't try blowing backwards through it.

 

[evanwellens]

Most likely but not exclusively it could be floating debris in the fuel tank getting sucked into the outlet blocking it off.
Next time it happens pull the fuel line from the item closest to the fuel tank and blowback hard through the tank.
Problem goes away for another 20 minutes or so = trash build up.

Note the fuel pump has a check valve on it so don't try blowing backwards through it.

Thanks for the reply. If that were the case I should see the fuel filter empty no ? And it doesn't.

 

[evanwellens]

Does it still happen if you loosen the gas cap?

I haven't tried that, but I shall

 

[evanwellens]

I haven't tried that, but I shall

Loosening ( even removing ) the gas cap has no effect.

 

[bertsmobile1]

Thanks for the reply. If that were the case I should see the fuel filter empty no ? And it doesn't.

I did not bother to tell you how to check for the purpose of exercising my fingers
If you can remember your high school physics you will understand that if the fuel line is blocked off at one end nothing can flow through it unless the pump is powerfull enough to collapse the line thus reducing the volume or air is passed back up the fuel line to replace the fuel drawn through
Remember the glass inverted in a sink full of water then lifted out experiment ?

If people do as they are asked rather than questioning it then people who know can work out what is wrong a whole lot faster and they end up back on the lawn rather than on the keyboard.
I could be right or I could be wrong but no one knows till what I asked to be done is done .

 

[evanwellens]

I did not bother to tell you how to check for the purpose of exercising my fingers
If you can remember your high school physics you will understand that if the fuel line is blocked off at one end nothing can flow through it unless the pump is powerfull enough to collapse the line thus reducing the volume or air is passed back up the fuel line to replace the fuel drawn through
Remember the glass inverted in a sink full of water then lifted out experiment ?

If people do as they are asked rather than questioning it then people who know can work out what is wrong a whole lot faster and they end up back on the lawn rather than on the keyboard.
I could be right or I could be wrong but no one knows till what I asked to be done is done .

OK I guess that makes sense. Thanks for the reply. I'll dump the tank and air hose the line after the fuel pump ( and maybe filter ) .

 

[evanwellens]

OK I guess that makes sense. Thanks for the reply. I'll dump the tank and air hose the line after the fuel pump ( and maybe filter ) .

Emptied the tank , ran engine dry , blew out the line , cleared the fuel filter , vacuumed out the tank. Seemed to do the trick, in fact I don't recall the mower running with such vigor in quite some time.. So thank you !!

 

[bertsmobile1]

I can assure you this was a very long & painful lesson for me to learn in the first place.
Lots of warranty work making me look stupider than I am already before I strained a tank and found all the trash that was invisible when there was fuel in the tank.

When the fule supply is restricted but can almost keep up with demand, the level in the bowl drops
That means the work the air flow has to do to get fuel into the engine is just that little bit more so it runs just a little bit leaner .
Not lean enough to surge but lean enough to be low on power till it either surges or starves.
You will need to add tank cleaning to your scheduled servicing at 1 to 2 seasons less than the time you have had the mower .
Happy mowing