Riding Lawn Mower Dies After 15/20 Minutes - I've tried everything I can think of

[avj300]

Hello Everyone,

I have a 2005 Murray riding lawn mower, model 425001X8C with a Briggs and Stratton 31C707 Type 0175E1 engine that is causing me to lose my hair much faster than I'd like. A few weeks ago the mower began to slowly die while mowing grass with the engine warm. The mower would start right back up again but when the PTO was engaged would die again a few minutes later. The first thing I tried was a new fuel filter and a carburetor disassembly and cleaning. The problem persisted so I began troubleshooting the mower and believed that the coil was failing me when it got warm. I replaced, and properly gaped the coil with a genuine Briggs part and the next time I took out the mower it quickly died again. Next was a new, properly gaped spark plug. Same issue. Then, searching through the forum, someone recommended that the safety switches might be the problem. To be honest I have only replaced the seat switch, but I have zip tied the PTO switch and Brake/Clutch switch to fake the Mower into thinking the PTO is never engaged and the brake is always engaged and the problem persists.

I have also tried cleaning out the vent in the gas cap, running the mower without the gas cap install at all, verifying the oil level is within specification, adjusting the valve clearance and ensuring that I do not have a locked up bearing on the deck by spinning the blades by hand with the mower not running. The mower has a brand new battery that starts and runs my cub cadet with no problem.

Additionally, I pulled the flywheel to verify that the flywheel key had not sheared and it was still in one piece.

I have also checked the spark right after the mower dies thinking that the new coil might also be bad. I am still getting nice blue spark right after the mower dies.

So to recap:
New Fuel Filter
Carburetor Cleaned
New Battery
New Coil - Gaped
New Plug - Gaped
New Seat Switch
Valves Adjusted
Oil Full
Gas Cap Vent Cleaned

And the mower still quits on me after 5, 10, 15, sometimes 20 minutes of mowing. The PTO doesn't have to be engaged to die and if you're really fast you can turn the throttle all the way down to turtle and you can save it from dying.

Other points of interest about the mower (not sure if they are related or not), the mower doesn't like to start when choked. Normally we have to play with the throttle position while turning the key to get it to run. The mower backfires after use, almost every time. These are issues we have been living with for years so I don't believe the are relevant, but don't want to rule them out.

So, does anyone have any ideas?

Thank you!

 

[ILENGINE]

Sounds like a fuel restriction. Could be something in the tank cutting off the fuel. or grass or other stuff actually in the fuel line restricting fuel flow. You are not getting enough fuel to keep it running with the extra load of mowing.

The choke issue could be that the choke isn't getting closed all the way if this mower has the further up choke position on the throttle control. The after fire is normally due to the solenoid on the bottom of the carb, but could have other causes not related to the engine.

 

[atonys]

Everyone wants to suggest a dirt restriction in the fuel tank. I have a similar situation on my 1998 Briggs and Stratton, and like you, have replaced so many parts it is almost a new mower. My brother had the best suggestion so far, and it is my next step: To dribble water into the intake with the engine running in a warmed up state. This will steam any carbon deposits from the valves and seats. Short of a dirt restriction in your fuel tank or lines, that may be the next step for you as well.

 

[avj300]

Thank you for the replies and suggestions. I pulled the fuel line from the carburetor to the bottom of the fuel tank. I split the lines a the fuel filter and blew each one out with the compressor with a rag over the open end. Each flowed air through with no issue and there was little to no deposits on the rag. I also blew air through the nipple in the bottom of the dank with similar results. Put it back together, rode it for approximately 20 minutes and she died again.

As far as the water in the intake thing, this scares me. Seems I have always learned that we try to keep water out of our air intake system... Don't get me wrong, I'm willing to try just about anything at this point, but I'd like for some others to weigh in and say this isn't a bad idea.

I did forget to mention in my original post that I did do a compression check on the motor and it seems like it is very high, so there may very well be excessive carbon build up. I couldn't find a spec for engine compression but my tester was reading about 140 psi. Seems I should be running premium gasoline with that kind of compression. See the photo below. Does anyone know what the compression is supposed to be on these 17.5 hp engines?

Thanks again!

 

[DJ660]

Remove fuel solenoid from bottom of carb..... Make sure the black cap on the end of solenoid plunger that blocks off the main jet is not swelled up and loose. If its easily removed that's most likely your issue. When engine is running the main jet is pulling fuel it pulls cap off and blocks jet.... engine stops... operator turns key off and solenoid plunger goes back out and cap is pushed back on and engine starts right back up. Check this out and please post results.

 

[Tinkerer200]

Well it depends on what carb it has whether there is a removable tip on that plunger. Most common ones here do not BUT the solenoid may be failing or wiring may be the problem. I would remove the solenoid, depress the plunger, wedge a tooth pick beside the plunger to hold it depressed, break off tooth pick, re-install and see what happens. That way if it isn't solenoid related, you haven't ruined the solenoid.

Walt Conner

 

[mechanic mark]

Intermittent problem, check all wiring by hand, especially all connections & ground straps & cables from engine to chassis making sure everything is tight & secure & rust & corrosion free.

https://www.briggsandstratton.com/n...nemanuals.html?searchrequested=31c707-0175-e1

see pages 4 & 14, you will need engine code number & Walbro or Nikki carburetor, items 947, 947A, 947B are solenoids.

https://www.google.com/search?sourc...oq=b&s 694393&aqs=chrome..69i57.33666j0j8just an example by googling B&S 694393

 

[avj300]

First I'd Like to again thank everyone for taking the time to respond and help me fix this issue. I know you all probably have better things to do than guess at fixes to my problem. I sincerely appreciate the support!

In response to DC660's question, the black tip did come off of the afterfire solenoid without a whole lot of tugging. There was some resistance provided by the knurled end of the solenoid plunger shaft, but it did pop off fairy easily. Not sure if the main jet has enough suction to pull it off or not...

Tinkerer200 - Who would have thought that a broken toothpick would "solve" my problem. I did as you suggested and pushed the plunger of the afterfire solenoid down and broke a toothpick off to hold it in place. I started the mower and let it run with PTO engage (since most of my safety switches have been disabled at this point) in the driveway for a good 30-40 minutes. After which I jumped on it and "mowed" a large section of my yard, and the mower only died on me once when it ran out of gas. I used the term "mowed" loosely because I have been "mowing" small sections of the yard pretty much everyday on my 20 minute jaunts to try to troubleshoot the mower. So I was not getting very much resistance due to grass at the blades. All in all I ran the mower for just over an hour with no issues!

So now my question is, what's the permanent fix? I see in my wiring schematic that the afterfire solenoid is an optional part and therefore Murray didn't feel the need to give me a part number. I can't seem to find a replacement by doing a google search. Since my mower has been backfiring for years now, can I just take the black tip off of it and disconnect the wires? Or maybe find a bolt with the same threads and remove the solenoid all together?

Thank you all again for the assistance!

 

[bertsmobile1]

The solenoid can be replaced, but they are not cheap.
So before you do it double check the wiring to it to confirm it is the solenoid and not a broken wire or bad earth.

Down here I cut the plunger off which means you have to throttle down to stop or you get a change the undies bang from the unburned fuel filling the muffler when the mower is turned off.
I also fit in line fuel taps and advise owners to starve the mower off when they have finished mowing.
You can replace it with a bowl bolt.

Caveat on both of the latter is in some states it is an EPA requirement and dissableing it carries very heavy fines on the off chance you should come to the attention of the relevant authorities.

 

[Tinkerer200]

It appears from your experience that the problem is the solenoid, the wiring to the solenoid from the ignition switch OR the switch. I think someone posted a way to test the solenoid but I don't remember it. I expect the solenoid coil is failing. The Safety Switches would not normally be a part of this circuit. They would be in the Ignition Circuit.

Since I THINK the solenoid is part of the Emissions Package required by the Fed, I will not recommend you do anything other than replace the bad component. I suspect the solenoid but don't know for sure and they are relatively expensive. I have always had a supply of good used ones so have never bought a new one. From what you have said it is not sucking the rubber tip off the plunger. You must have a Nikki Carb. 9 out of 10 31 series engine carbs here are Walbro and have a pointed steel plunger, no rubber tip. IF the carb bowl is held on by screws around the outside of the bowl, it is a Nikki and the solenoid part number is 695423. IF the bowl is held on by the solenoid, it is a Walbro and the solenoid is 694393. The plug replacing the solenoid is 691657. I have heard some say they just cut the plunger off.

You can reduce the back fire (after fire) which the solenoid is intended to do by letting the engine idle for 20 seconds or so before shutting the engine off.

Good luck,

Walt Conner