At a loss... With my mower that runs for awhile, surges for a bit, then dies.

[bcollins3481]

Hey everyone! I have a few years old Cub Cadet wide area push mower [CC760ES (12AE76JU010)]. It has been giving me issues since the middle of the last mowing season.

What started to occur was the mowing operation was going like normal but after about 2 hours into mowing (just about done with my yard), it started to surge and then eventually died. I have to let the mower cool for a bit before I can start it unless I open the choke, which works for a bit but then eventually wont run at all. Over the last year the symptoms have just gotten worse, I'm down to about 15 minutes of mowing. The heat does seem to affect the mowing time and also how long it takes before I can mow again.

At first, I changed the oil and spark plug. While I changed the spark plug I used an aftermarket product that is meant to clean the engine by spraying into the spark plug cavity with the engine off and then wait 15 minutes before you start the mower. When the engine was started I was sure to believe the EPA was having alarms going off to send a helicopter, luckily the black smoke died before they arrived. This process didn't seem to do anything.

This year, I have changed the coil assembly, the coil assembly charge (part under the flywheel), new air filter, new fuel line and fuel filter. I also removed the carburetor and it was clean as a whistle. I don't know about the tiny valves being clean but the bowl was clean. I tested the fuel solenoid and it retracted fine while it was cold. What I did notice though was the o-ring on the solenoid was broken apart so I replaced it.

The most important detail I can think of though is when the engine starts to surge, I can very gentle apply a little of the choke and it steadies out. However, this only works for say like 5 minutes, basically enough to turn the mower back around and head toward the house so I'm not pushing it down the street like an idiot.

I have tested the gas cap vent too by running with it 90% off, didn't make a difference.

My extremely patchy lawn is getting more than usual looks from my neighbors, any suggestions would be totally awesome. Otherwise, I will be on the mowing 1/7th of my yard everyday of the week.

 

[bcollins3481]

Ok, a little further diagnosis... As the motor is surging the governor arm on the carb is moving rapidly back and fourth. If I use my finger and prevent the governor link from going to far forward the engine seems to idle properly. I have no idea what the means though.

 

[ILENGINE]

Symptoms sound like a fuel restriction issue. Could there be something floating around in the tank that gets pulled down on the fuel outlet of the tank when the tank starts getting to a certain level.

 

[bcollins3481]

Symptoms sound like a fuel restriction issue. Could there be something floating around in the tank that gets pulled down on the fuel outlet of the tank when the tank starts getting to a certain level.

The fuel level doesn't seem to affect it, near empty of full it does the same thing. I haven't noticed one event taking longer or shorter to when it starts to surge.

As for something in the tank, I don't believe so. When I replaced the fuel line I gave the tank a decent bath, it's also pretty visual and I've never seen anything in the out spout in the past.

One thing I thought was strange when I removed the carb, I detached the hose that goes from the carb to the gas tank at the top (not the fuel line) and gave it a good blow. I gave it hell and it didn't seem to release much air into the tank with the cap off. I'm not sure what sort of air restriction I should expect, but any air making it into the tank didn't seem perceivable.

 

[ILENGINE]

You have the emissions tank. When the engine quits loosen the fuel cap, and see if it will restart. It sounds like the charcoal canister attached to that line may of bricked. It seems like if those vent connectors in the tank get fuel contaminated they swell, or brick the charcoal and don't allow air to vent into the tank causing the problem that you are seeing. That type of system is designed to operate under a slight vacuum, but can cause problems, especially if the fuel filter has been replaced with one with a finer filtering material.

 

[bcollins3481]

You have the emissions tank. When the engine quits loosen the fuel cap, and see if it will restart. It sounds like the charcoal canister attached to that line may of bricked. It seems like if those vent connectors in the tank get fuel contaminated they swell, or brick the charcoal and don't allow air to vent into the tank causing the problem that you are seeing. That type of system is designed to operate under a slight vacuum, but can cause problems, especially if the fuel filter has been replaced with one with a finer filtering material.

Thanks for the response! I had an opportunity to test it, and the engine still stalls with the cap loosened after it starts to surge. After the mower dies I was able to start it right back up with the gas cap tight, or loosened. After doing this 3 or 4 more times, it wont start until it cools down. Otherwise, the gas cap didn't seem to change how it operates.

If the hose that tries to pull (push?) air from the gas tank collapses, or can't pull any air, would it matter if the gas cap was tight or loose?

 

[tyraen]

I haven't worked on a Cub, but these engines all have feedback systems built around spring tension. I saw a video where the engine had the tension poorly set on the governor arm coupled with some loose connections to the linkages that was creating some kind of a cyclic feedback loop. The loose linkages allowed for too much play and the loose spring allowed the governor to "bounce" and the timing would lag behind the carb's reaction. The engine would then starve, then surge, then starve, very rapidly. I don't know if it's correct, but its such an easy thing to check for I figured I would mention it. Sometimes, on the composite plastic arms, the metal links wallow out the hole it goes through until this happens.

Good luck!

 

[bcollins3481]

I haven't worked on a Cub, but these engines all have feedback systems built around spring tension. I saw a video where the engine had the tension poorly set on the governor arm coupled with some loose connections to the linkages that was creating some kind of a cyclic feedback loop. The loose linkages allowed for too much play and the loose spring allowed the governor to "bounce" and the timing would lag behind the carb's reaction. The engine would then starve, then surge, then starve, very rapidly. I don't know if it's correct, but its such an easy thing to check for I figured I would mention it. Sometimes, on the composite plastic arms, the metal links wallow out the hole it goes through until this happens.

Good luck!

The symptoms do match, however, I don't think this would be it mostly due to the fact that heat or mower runtime seems to be very related. I can only see it being related if the heat is causing the plastic arms to become more pliable but seems pretty far fetched. I will try my best to track this down as a possible cause but I'm not that hopeful. I do appreciate it though!