Lawnmower Engine Problem

Eric Patterson

Eric Patterson

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I have a 30 year old Toro rear engine mower I use to cut the grass at the workshop. The mower is original and I'm on the third engine. Toro built the frames and transmission like a tank so it has withstood the test of time.

Lately the motor has been sputtering and missing. Not all the time but very repeatable. It starts fine, runs a minute then starts missing and smoking (black and blue). It will die and I'll restart it several times. RPMS are way low since it is missing. But, if I keep restarting and running it, it eventually starts to run better until it runs perfectly. It takes about 10-15 minutes to warm up and run like nothing is wrong. I took it to a repair shop and they cleaned the carb. That didn't fix it. I thought maybe a bad coil but the mechanic said a bad could runs better cold and worse when warm, just the opposite of my mower's behavior.

Any ideas on what the problem might be?

Eric

Toro-wheel-horse-1.jpg
Not my mower but one just like it. My kids tell me I look like Forrest Gump on it, but I tell them Forrest drove a Snapper. Dumbshits :)
 
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Could you have water in the tank?

Other than that, a bad coil was my first thought.
 
The mechanic was supposed to flush the fuel system. I need to shine a light down there to check for that, but I don't think the miss would go away after warming up if water was the cause.

Thanks.

Eric
 
Check the valve lash when cold. Check the valve lash when hot. The valves may not be fully seating when cold, but after the block warms up and expands more than the valve stems, the valves will fully seat.

Sometimes a head gasket will leak when cold, seal when warmed up, Check compression hot and cold
 
Dave

I plan on checking compression this evening. I'll have to look but I don't know if they are overhead valves. Meaning they may be a PITA to work on. I hope its something simpler.

Thanks.

Eric
 
Eric,

Have fuel lines been checked? Do you have an inline filter? I get sludge out of the gas tank and low fuel delivery from the tank on my John Deere STX38.

Rick
 
Fuel filter is clear. I'll check flow tonight. When you had sludge in your tank did it just affect the motor before it was good and warm? I'd think that would persist regardless of engine temp.

Eric
 
I think Dave is on to something I would check that and compression. I had a Kawasaki that would be very hard to start but once running would smoke then clear up. Compression was 65-70 if I remember right I was honestly amazed it ran like that.
 
Okay here is the latest after looking into it a bit more today. Gas tank was very clean and filter as well. Fuel flows just fine. Assuming the mechanic did clean the carb, and I believe him, I think I can rule out a carb issue, or at least put it down the list. Spark plug was a bit dirty but I've seen plenty worse. No signs of wear. However, the gap was set to .02 and not .03 like every Briggs flat head I've ever owned. I re-gapped it. Compression cold was 123 psi. After running it for about 30 minutes it climbed to 130. I don't believe 7 pounds when cold is causing the miss.

But the weird thing was I didn't have the miss today, and no smoke. So either it was the spark plug gap, which I kind of doubt, or it is an ignition issue that has decided to stop. I bet it will be back. I'll let you know.

Appreciate all the input.

Eric
 
The misfire is back. Was at the shop last night so I started the mower to see how it ran because I don't believe the .20 gap was the culprit. Sure enough it ran okay for about a minute, then started missing and belching out thick blue smoke, then it died. I pulled the plug and it was wet with oil. I checked spark and it was getting a steady blue arc. I put it back in and restarted it and it kept misfiring. I let it run for about 20 minutes and it cleared up, as always. I checked spark again and it was the same blue arc I saw when it was misfiring. No oil either.

So with that said I don't think I have a magneto issue. I don't think I have a carb issue either because it seems so temp dependent. The compression test I did earlier doesn't suggest that being an issue either. If you recall the compression was only 7 psi higher when the motor is fully warm. So now I'm thinking it is a valve issue. Maybe a sticking oil ring too. I think I'm taking it back to the mechanic this week. Too many other projects ongoing that I don't want to take time from when I can pay someone to fix the mower. Depending on what the mechanic says I might scrap it. After 30 years I'm ready to get a more modern mower for the shop. One that I don't have to f around with anymore.

Eric
 
Eric Patterson said:
The misfire is back. Was at the shop last night so I started the mower to see how it ran because I don't believe the .20 gap was the culprit. Sure enough it ran okay for about a minute, then started missing and belching out thick blue smoke, then it died. ,,,,,,,,,,,,, So now I'm thinking it is a valve issue.

Eric
Click to expand...

From my perspective way over here in my Lazyboy,,,,,,,,,,, I suspect you may have narrowed it down to the culprit.
 
Dave

If it is a valve issue, why all the blue smoke? Does that cause a vacuum action sucking oil into the cylinder area?

Eric
 
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Eric,
Pretty much what Pete said, excessive valve guide clearance. Pulls oil past the valve stem, to the intake manifold where it then enters the cylinder. As the valve stem warms and expands, the clearance around the stem decreases thus reducing the amount oil getting past the stem.

Double edged sword; exhaust pressure leaking past the exhaust valve stem, leaks into the crankcase causing slight pressurization. Excessive clearance around the intake valve stem, will allow the intake manifold vacuum (aided by the slightly positive crankcase pressure ) to pull oil thru to the intake manifold, where it gets combined with the fuel mixture entering the cylinder.
 
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Dave & Pete

Dropped it at the shop, AGAIN. Mechanic going to tear into it deeper. He says if it is a valve problem he'd expect to burn oil at all times. Me, I'm shopping for a new mower. Tired of loading it up and tired of it being at the repair shop while the grass gets too tall to mow.

Eric
 
Looks like I forgot to post the rest of the story. Took the mower to my mechanic who tore into the motor. He found worn valve guides and a scarred cylinder wall. These explained the oil consumption. The cost to replace the motor was over a grand. Given it was aa 30 year old mower I left it with the mechanic who will scavenge parts. I bought a new Big Dog zero turn. It takes less than 30 minutes to mow the lawn a the shop. It used to take about an hour. I'm kind of glad the old mower bit the dust now :)


Eric
 
Glad you like the new mower. I put off getting a zero turn for my place for almost 3 years. I used to push mow almost an acre.....it would take me usually about 4-5 hours a week broken up into multiple days...do the front one day, back another and back back another. When I got my zero turn, I can mow the whole acre or so in about an hour. I kicked myself majorly for being stingy and not ponying up the monies. WELL WORTH IT!
 


" The largest irrigated crop in the U. S. - 40 million acres, the size of Florida - is grass. It's the most powerful domesticated plant ever. As a crop it offers nothing. You can neither sell it nor eat it. It has no function except to make us feel better about ourselves."

SEEDS OF DISCONTENT Are our lawns plotting against us? by Bill Heavey F&S 2019.
 
Vince, out here when you built a house they planted grass seeds. Now we have many sod farms [ instant grass lawns ]. News article, water shortage going on. Lowes owner using 7 Million gallons of water this year. GREEN GRASS $$$$$ here.
 
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