I think I fixed my mower?

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Dargin
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I think I fixed my mower?

Post by Dargin » June 17th, 2020, 10:07 pm

So, my last cut didn't look too hot. Actually, it was the worst I've ever seen it, and right when i felt I was finally upping my blade sharpening game. The lawn now has that tan cast from shredded tips...ready for disease...ugh.

When i mowed the lawn the engine didn't sound right. It was pulsing a lot. I've since read up on what that issue could be and have been going down a checklist of troubleshooting.

I siphoned the gas out, ran it dry, and filled it with Super. I also put a new air filter on. Started it. A little pulsing, but also an overall different sound, weaker, like it wasn't getting to full power, but steadier than the initial pulsing from the previous cut. Also a new noise, almost like a small metal rattling; I wouldn't call it a knocking. This all lasted for about 2 minutes and the engine cut out. Continued attempts to start failed; wouldn't run for more than 5 seconds.

I just got a new replacement spark plug.
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My manual says .020 gap. I tested the old one and it was .035.
I tapped the new one down to .020, popped it in, and the engine started up with a couple pulls. I -think- it's running ok now. I let it run for 10 minutes. Doesn't seem to be pulsing anymore and no weird noises.

However, when I was replacing the spark plug I also tried to look at the carb; new territory. It wasn't entirely easy as I couldn't remove the engine cover due to very stripped screws. The carb is a plastic Briggs and Stratton.

Image

I wasn't able to get the carb off today, but I was able to poke around and see the float and needle, and clean some pretty thick dust/debris off the outter moving parts...and spill some gas. I think I figured out how to finish removing it now; just need to remove the choke and throtal linkages and pull. Gonna drain the engine again give the carb a thorough cleaning.

So I guess I just don't know what really helped (if the problem's REALLY solved); the very light carb cleaning or the spark plug?

Can a bad spark plug really cause the series of symptoms I described?

Appreciate any thoughts.

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MorpheusPA
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Re: I think I fixed my mower?

Post by MorpheusPA » June 17th, 2020, 10:27 pm

I'm trying to limit my carbs.

:-)

https://itstillruns.com/symptoms-incorr ... 81478.html

Most importantly, "Spark plugs that are gapped incorrectly can cause an engine to miss, or run erratically, especially during idle."

So my statement would be "yes," which was my guess right off the cuff. You were trying to jump a spark gap of 0.035 with a spark designed to jump a gap of 0.02. An air gap is linear, so the voltage had to be almost twice as great. Your cylinder timing was way off.

It's no wonder it runs better now, or that your carb was crapped up. And I don't even know that much about engines, just the basics. :-)

Dargin
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Re: I think I fixed my mower?

Post by Dargin » June 17th, 2020, 11:02 pm

I thought I smelled ketones. ;D

Thanks for the feedback. Been living in a bubble with this problem for a couple days. I guess maybe the gap on the old one widened over time as the electrode degraded. It ran pretty well for a year on that spark plug.

Hopefully no surprises tomorrow...ha!

Appreciate the Info, man.

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andy10917
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Re: I think I fixed my mower?

Post by andy10917 » June 18th, 2020, 8:41 am

Once upon a time millions of years ago in my college days, I worked summers as a small-engine (mostly lawn mowers and lawn tractors) mechanic. Most of what you did is what is called a tune-up. It's an annual practice for me on my Honda HRX-217.

Can an improperly gapped spark plug cause problems? Yes, but generally it shows issues mostly when other things are out of spec.

Many of the plastic carbs on Chinese-made B&S lawn mowers are not tunable,

agn015
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Re: I think I fixed my mower?

Post by agn015 » June 18th, 2020, 8:58 am

How old is the mower? Is it new or used? I've always bought used mowers and make sure to do a full tune-up the day I buy it and then annually as Andy suggested. I'm just a little ocd and actually keep track of runtime hours with a cheap hour meter/tachometer but that's not necessary if you only mow 1-3k sqft.

I also started using sea foam in the gas can at the pump whenever I fill it. Just 1-2oz/gallon to work as a stabilizer and I think it helps keep everything clean and flowing properly. It could just be snake oil, but I haven't had a fuel issue since I started using it.

Good luck cleaning the carb! It usually isn't complicated. Take pictures. I like to use the wire from the center of a twist tie to make sure all of the orifices are clear.


Dargin
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Re: I think I fixed my mower?

Post by Dargin » June 18th, 2020, 3:42 pm

Good stuff, thanks.

Agn015, the craftsman mower is about 4 years old. I got it used from a relative a few years ago. I've only changed air filters a few times, spark plugs twice (now) in that time. Oh, and I've kept the oil full. More on that in a sec...
I'll make sure to stay on top of this stuff from now on.
Thanks for the twist tie idea, and I'll read up on the seafoam. Taking pics has been a big help so far.

Andy, I think the HRX is -just- the replacement part I need. :D

I'm grabbing carb cleaner tomorrow and getting to it. Today I just practiced disassembling and assembling. I feel more comfortable with it now.

I really don't want to ask too much, but there is one other factor that I think might play into this. I only made the connection today. Over a month ago I accidentally overfilled the oil. Honestly I don't recall by how much, and I didn't understand the many issues this could cause. Right now it's about a 1/2 inch over the maximum line on the dipstick if that means anything. Mowed about 12k since overfilling. Seemed fine. I'm a dolt...

So I guess I'll add siphoning down the oil to tomorrow's list.

Today I tested it another 10 minutes. Started right up, but I did get a couple noticable drops in power.

I'll post progress tomorrow.
Thanks, guys.

Dargin
Posts: 246
Joined: September 29th, 2017, 12:42 pm
Location: Central Mass
Grass Type: Northern Mix
Lawn Size: 1000-3000
Level: Some Experience

Re: I think I fixed my mower?

Post by Dargin » June 20th, 2020, 1:51 pm

Got the carb taken apart and cleaned it with Gumout. Got all the jets inside the cartridge. It really didn't look bad inside. No residue.

Got most of the oil out. Pretty ugly looking. It had a grayish tint, kinda like graphite. Read some not so great things about that; maybe cylinder damage, but still reading.

Image

Filled it back up with SAE 10W-30; been using the same kind since day one. Started up on 2 pulls. To me it sounds good. Stronger and steady.

Only thing I noticed was a bunch of short sizzling sounds around the engine when I cut power; like tiny water droplets on a hot surface. I don't see or smell anything unusual. It might have made these noises before and I never noticed.

Still doing some reading, but hopefully I'm back in business.

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