Help diagnose a riding mower that won't start

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Hi folks,

Hoping I can get some help with lawn equipment and small engine debugging here. Given the wide range of interests we have I expect someone might have experience with these things.

I’ve recently acquired some riding mowers, and this red one was working when I bought it (seller demonstrated it running) but it now won’t start when I brought it home.

Let me also say that I am handy and I have done some work on cars before, but I am pretty new to debugging an engine itself. I have been reading and watching a lot of YouTube, and I have a decent understanding of how things work now, but I might also be overlooking something dead simple, so please leave no stone unturned.

Specs:

Troy Bilt 13AX60TG766 Riding Mower, 2006 era. Engine inside is a Kohler Courage 19.

Symptoms:

  • Battery is dead so I have the machine hooked up to a jump starter or jumped from my truck.
  • Engine will crank but will not start. While cranking I hear a squeal/ whine from the rear of the unit where the battery is or would be located. And after a few seconds of cranking there is a buzzing sound coming from the engine.

I believe I am starting the unit correctly - the PTO is disengaged, the parking brake is on, the choke is on, the unit is in neutral.

Steps taken so far:

  • Opened up air filter cover, removed air filter, can see carb butterfly. Confirmed that it is closed with the choke engaged. This rules out a loose linkage.
  • Disconnected fuel line, yes we have gas going through the inline filter.
  • I removed the fuel solenoid and verified that gas is leaking out of the carb bowl, and that the fuel solenoid actuates smoothly. I hear the click of the fuel solenoid when I turn the key on. This confirms that the fuel solenoid is operating properly.

In my later steps of debugging, with some of the items taken off as you will see in this pic, I did get the engine to sound like it was running for a few hits during cranking, and some white smoke came out of the exhaust, but the unit still did not run. I later learned that running the unit with the carb opened up and no air filter on may not have been the smartest move, and that I will likely have to put a new gasket behind the carb now that I have taken things apart there.

Anyways here is the pic of the most disassembled that I got the unit:

Mower
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I’m wondering if it might be a fuel issue - like if the tiny amount of gas that was in the tank before is suddenly bad? But it ran fine when the seller demonstrated it running. I did add more gas to the tank but did not drain the bit of old gas.
Otherwise something to do with the spark plug or ignition coil?

Mostly I am trying to figure out what could have gone bad in the 90 minute likely bumpy road trip this mower took to get to my house. I have ruled out all of the “major problems” I have found on the internet and need help with deeper debugging.

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Wow that looks familiar… Michael's 2005 MTD Super Bronco

Have you checked for good spark? Pull the plug, hold the outside of the plug to the engine to complete the circuit, look for strong and consistent spark.

Also check for junk on the plug. In my experience, every time I’ve thought I need to clean and gap the plug, I really just needed a new plug.

Squeal/whine near the battery while starting I can only guess is the belt, which goes around the pulley on the motor shaft and then back to the transmission in the back. When I bought new belts for mine on Amazon, they were a little bit too short and the transmission wouldn’t engage. I found OEM belts at Home Depot just down the road and those worked fine.

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Thanks for the quick response. Amazing that you converted a similar unit to an EV :slight_smile:

Haven’t yet, but that was the logical next step for me.

I can definitely do this tomorrow. Just saw what you say done in a video.
I was wondering if I needed an inline spark plug tester, but I guess that is a good first step. If I have no spark, then it would lead down the path of figuring out whether it was a bad spark plug, or if the plug was good but it wasn’t getting any electricity (from the ignition coil, I believe).

On a side note, do you know if most riding mowers take the same size *starter* battery? I will need to get a new battery once I get this guy running, and the one I pulled only says "Small Engine" on it, it does not have a size code like I am used to with car batteries.
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I got replacement batteries at Home Depot or Lowes. I don’t know if most are the same size, but there was something that fit there.

You have to buy a lot of replacement spark plugs before it’s cheaper to buy a tester. That’s my theory now. :smiley:

You can also check for spark from the lead, without the plug in it. If you get spark from the lead but not from the plug, the plug is definitely toast. If you get no spark from the lead, then yeah look upstream.

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Is your fuel filter clean? Brain storming.

I have a troy bilt horse xp so also curious.

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Michael hit the nails I was doing to mention. You can look at the plug and do the spark test he mentioned and hopefully there’s a spark from the center electrode to the bent arm leading over the center electrode. you don’t want to see a spark going sideways or down the ceramic insulator. I wouldn’t expect the electronics which generate the spark to fail so quickly after purchasing.

But, getting the choke and throttle figured out to start the machine can be tricky and often results in fouled plugs which then need a deep cleaning or replacing. The previous owner might have known by instinct the right amount of choke and throttle for the current outside temperature.

Odds are it’s the plug which is fouled and can’t get the fuel ignited. Also check to see if the fuel is fresh.
The previous owner might have had it running after starting it with starter fluid and had the engine hot when it was demoed for you.

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Now that it’s morning and I’m possibly awake… :grin: Measure the resistance of the plug with your multimeter. If it’s not between 500 and 5000 ohms, replace it.

What I was taught was if the resistance is too low, the spark doesn’t last long enough to reliably ignite the fuel; if it’s too high, the spark might not be strong enough or not form at all. I don’t know whether that was truth; what I understand is that the spark plug is the resistor in an LR series circuit, and the magneto as a pulse generator is basically the voltage source and inductor.

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Would that be measured from the connection point on the outside of the plug to the center pin? Or is there connection between the conductor and the chassis ground of the plug?

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Thanks for everyone’s input.

I only had a few minutes today before I had to bring everything back into the garage due to rain.

In those few minutes I pulled the spark plug and sure enough it is all black and gunked up and the resistance is at least 12k ohms, if not in the megaohms (getting the multimeter probes onto the gunked tip area is difficult)

IMG_4132
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Amazon order for a Champion 3071 (equivalent) plug is submitted. More next week when it arrives. Lots of rain this week anyways so couldn’t do much even if I wanted to.

Haven’t taken it off yet, so can’t say, but it is letting gas through, so at least it is not gunked up.

This is the video I used, fast forwarded to the good parts :slight_smile:

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Many many many moons ago when my mini-bike Briggs&Stratton plug would foul I used to spray it with carb cleaner(or was it just white gas?) and then take a wire brush to the end and many times that was enough to get-er running again. YMMV and new is always better.

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Well, I got the new spark plug in and the unit still won’t start, it will crank, white smoke comes out of the exhaust, and the engine will “cough” a few times, but it never catches and gets fully spinning.

Also, with the old spark plug taken out, I plugged it in and tried starting the unit and got zapped, so we’re getting voltage to the plug.

We have fuel going to the carb and we have spark. Logic says that we’re in the land of deeper engine troubles now?

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White smoke while starting… Have you cleaned the carburetor?

(Incidentally, mine smoked shortly after it started but that turned out to be a bad seal in the carb that caused a gas leak that pooled gas on the top of the muffler. I feel lucky that didn’t get way more exciting.)

Sometimes if there is a bit of contamination in the carb, like oil, if you can get it started with starter fluid, running fresh gas through it for a while can clean it out…

It’s been a long time since I took the small engine repair class though.

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One long shot… If you feel around the head gasket while it is cranking you might feel puffs of air. That would be the gasket leaking, preventing good compression.

I had an old Briggs snow blower engine that I had to replace the head gasket on a couple of times. (car guy next door took one look at it and showed us the problem)

For the small snow blower engine it was a matter of pulling 5 cap screws (bolts) and putting in a new gasket. May be a bit more complex on the bigger engine.

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I would pull the plug again and look at it and look for signs of lots of fuel( ie too much fuel ). Really shouldn’t reak of gasoline nor should it be wet.

One thing I used to do was try to start with the choke and if that didn’t work then you have to try a few things since you might now have too much fuel in the cylinder and on the plug. one is to turn the choke off and crank it a bunch and if it tried to sputter to life quickly try giving it a little choke to see if you can keep it going. The other thing is to pull the plug, dry it with compressed air and then crank the engine a few times without the plug to get all the gasoline saturated air out.

Since it was running before you purchased, I’d still be on the side of learning how to start it. Also, do not give it any throttle when starting. It should be mostly finding the choke position.

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Doug you nailed it. I had it all the way up to the “choke” position and all I had to do was back off a step to “high” and it started right up. Then I can lower to about 50% and drive around just fine. It was late, as I just went back out for this test, so hopefully soon I can do a more thorough “field test” :slight_smile: soon.

For comprehensive continuity, here are the results from testing before I succeeded with the above:

I wasn’t specifically able to feel this, but the flywheel was blowing a lot of air onto my hand so it wouldn’t have been easy to.

I have not, I was in there before and fuel was getting through.

I used WD40 spray since I did not have starting fluid and the manager at Harbor Freight told me that’s what he uses. The crank but no start symptoms were the same as previously described.

Anyways, it runs now, and I got a new battery for it yesterday. (No Michael, not the kind of batteries you put in yours :slight_smile:)
I have to figure out the fix for the steering wheel slipping when trying to turn while standing still. I believe this has to do with a retention bushing/ nut/ fastener kind of thing that secures the bottom of the steering rod to the frame and prevents it from flexing and slipping. I’ll get in there to check it out in detail at a later time.

Thanks everyone for the detailed help. Another example of why I prefer here to FB.

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You can probably adjust the max choke position. I got rid of my gas engine so I can’t confirm, though! :smiley:

Ooh, I probably know this one.

There is a gear at the bottom of the steering shaft that can wear out; this happened to me.

https://www.amazon.com/gp/product/B005UATAHY

Good chance it’s the same as your unit.

Check the rack for wear too. In my case it was just the pinion and the rack was fine. I keep expecting mine to wear out again, because of the weight of the batteries I have over the front wheels, but so far it’s working. :crossed_fingers:

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The unit steers ok when moving though, so based on videos I saw I wonder if it is the flange holding the system into place. This is what I was trying to describe above, and your Amazon link conveniently showed me the related part, so now I have the vocabulary to articulate it:

https://www.amazon.com/MTD-741-04237B-Hex-Flange-Bearing/dp/B0017KAFMK/ref=pd_bxgy_vft_none_sccl_1/140-3269386-2572545?pd_rd_w=nVOdY&content-id=amzn1.sym.26a5c67f-1a30-486b-bb90-b523ad38d5a0&pf_rd_p=26a5c67f-1a30-486b-bb90-b523ad38d5a0&pf_rd_r=A2BXB5T3P8AMTWGJTQ7X&pd_rd_wg=g1OUr&pd_rd_r=a982c937-7728-4ca3-babd-6e9551a301c7&pd_rd_i=B0017KAFMK&psc=1

I’ll dig into it a little later.

I also got a Murray 425009x8 mower with a Briggs engine in it (from the same transaction), this is a 6 speed but doesn’t have a gas pedal, so you have to be on the clutch/ brake pedal any time you are not moving. It needs a new deck belt which I have on order. I have already run this one. Without a battery connected the engine runs a little rough and I’m not sure that the seller’s comment of “it should run more smoothly with a battery hooked up” makes sense. I’ll also dig more into it later.

Finally, I think I need to tighten up the braking on both units.

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FYI this is the steering symptom and fix that I’m referring to:

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So that bearing flange isn’t a bearing at all but instead is a bushing and it doesn’t look like it’s oil enpregnated brass so why not put a bit of lithium grease or bearing grease on that for a chance of a longer life.

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Oh yeah I forgot about that bushing. It’s been a while.

A bushing is one type of bearing. Its not a ball bearing, or a needle bearing, etc. But the shaft bears on it; it’s a bearing.

Because they would pick up and hold abrasive dirt, and mowing the lawn creates a perfect environment to get dirt in there. It should be dry.

It should be bronze not brass for longer lifetime, but nothing about this tractor screamed “engineered for the ages” when I pulled mine to bits and put it back together as a frankentractor.

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