Mower Repair Question

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mrbone
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Mower Repair Question

Post by mrbone »

I was hoping someone could help me with a push mower problem that has me stumped. It's a basic Briggs & Stratton engine. It starts fine and has good RPMs. Sounds like it's got full power, but when it hits grass it loses power and stalls easily.

I've tried:
* New spark plug.
* New engine oil.
* New blade.
* Disassembled the carb and cleaned out the gunk.
* Ran carb cleaner through the air intake.

Anything else I should be looking at?
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evan price
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Re: Mower Repair Question

Post by evan price »

Check to make sure flywheel key has not partially sheared, this will affect the timing of the spark and cause that problem.
Air filter should be clean and not over oiled if its foam.
If the carburetor has a float bowl make sure the tiny ports inside the nut are not clogged.
If the carburetor had a diaphragm make sure it's not pinholed.
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Re: Mower Repair Question

Post by sodbuster95 »

The grass is too tall. :wink: :lol:
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Re: Mower Repair Question

Post by glocksmith »

sodbuster95 wrote:The grass is too tall. :wink: :lol:
You're absolutely correct. Every Spring I see my neighbors out there with their motors bogging down and stalling because they let their grass get way too high and thick before cutting it. There are some of us in my neighborhood who have the foresight (and the motivation) to cut ours before it gets that out of hand. :D
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Re: Mower Repair Question

Post by pk47 »

glocksmith wrote:
sodbuster95 wrote:The grass is too tall. :wink: :lol:
You're absolutely correct. Every Spring I see my neighbors out there with their motors bogging down and stalling because they let their grass get way too high and thick before cutting it. There are some of us in my neighborhood who have the foresight (and the motivation) to cut ours before it gets that out of hand. :D
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Re: Mower Repair Question

Post by roughsawn »

Have you sharpened the blade lately? I know my mower (an old Toro built in 1994!) will act like that with a dull blade. Just bogs it down.
Sharp blade = no problems
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Re: Mower Repair Question

Post by Bruenor »

After talking to several dealers recently as I was shopping for my new mower, I've come to find out I should always be using pure gas without ethanol or alcohol free fuel stabilizer if I have to use ethanol blended gas in my small engines. (alcohol attracts moisture so you don't want it in your fuel stabilizer) small engines aren't designed for ethanol, and gas from the corner station will damage the engines, and fuel system components over time. several commented that ethanol gas keeps them in business. so Sta-Bil or Startron it is, for all gas that goes into my new mower, and other small engines, and I'll be swinging by the pure-gas stations to get pure gas for my small engines moving forward.

Best of luck with your engine repair, just wanted to pass on what several shops told me about caring for my new engine over the long term.

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Re: Mower Repair Question

Post by Tourist »

I don't know if this will help, but the mowers I used to use had a "flat flap" that was moved by air caused by the engine spinning. When the engine slowed, the flap was connected to the carburetor and sped up the engine to maintain the RPM. If this was disconnected, the engine would slow and stall under load.

Good luck and let us know the cure.
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Mr. Glock
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Re: Mower Repair Question

Post by Mr. Glock »

Your two articles focus on E-15, mostly, which is a booddoggle for Big Corn. It appears that even car engines built even fairly recently can have issues with E-15.

E-10 has been around for awhile, fuel stabilizer works well over time.
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Face
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Re: Mower Repair Question

Post by Face »

I have not worked on a B&S in over 10 years. What are they using for ignition on the current one? It sounds like a weak or bad coil - if they even have a coil.

Had that happen a few times on everything from outboards to my current rider with a Kawasaki.
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Re: Mower Repair Question

Post by glocksmith »

No grass cuttin today in SW Ohio. It's all under water.
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Re: Mower Repair Question

Post by screwman »

Face wrote:I have not worked on a B&S in over 10 years. What are they using for ignition on the current one? It sounds like a weak or bad coil - if they even have a coil.

Had that happen a few times on everything from outboards to my current rider with a Kawasaki.
That's what I was thinking, the coil. When all else has failed, it's the coil.
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Re: Mower Repair Question

Post by JustaShooter »

Mr. Glock wrote:Your two articles focus on E-15, mostly, which is a booddoggle for Big Corn. It appears that even car engines built even fairly recently can have issues with E-15.

E-10 has been around for awhile, fuel stabilizer works well over time.
I wouldn't have thought that E10 would be an issue for newer mowers either, but apparently it is. I guess the real issue is longer term storage where the alcohol in the fuel attracts water and starts breaking down and forming acids. So, use fuel stabilizer and drain & run the engine till it runs completely out of fuel before putting it away for the winter and it should be fine.
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Mr. Glock
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Re: Mower Repair Question

Post by Mr. Glock »

JustaShooter wrote:
Mr. Glock wrote:Your two articles focus on E-15, mostly, which is a booddoggle for Big Corn. It appears that even car engines built even fairly recently can have issues with E-15.

E-10 has been around for awhile, fuel stabilizer works well over time.
I wouldn't have thought that E10 would be an issue for newer mowers either, but apparently it is. I guess the real issue is longer term storage where the alcohol in the fuel attracts water and starts breaking down and forming acids. So, use fuel stabilizer and drain & run the engine till it runs completely out of fuel before putting it away for the winter and it should be fine.
There is always water in a gas tank (car, lawn mower etc). In the olden days, this would be condensation that rose to the top of the gas tank (one reason metal car gas tanks rusted from the top over time). Alcohol does absorb water, which plays out to what we see today because ethanol and water are more "irritating" to seals and plastics (and old boat fiberglass gas tanks...actually softens them over time) than just straight gas. Plus, gas tends to lose the light ends of the formulation over time, the lighter ends being what helps ignition. So, as I understand it, you have two issues here. One is the alcohol/water is more wearing on some parts and the second is today's gas can vaporize off easier, leaving increased gunk and creating difficulty with ignition. It's also lower octane today than in the past (high 90s and 100 was pretty common before 1975's change to no-lead gas), so less margin for degraded gas too.

Alcohol has less energy per unit that straight gas too. So car that go 400 miles on a tank of E-10 can only go about 300ish on a tank of E-85. That data is pretty close for a flex-fuel truck I used to own, and came right from the owner's manual.

The big issue with E-15 is that it increases the alcohol level over what cars and other items have generally been designed for, for no other reason than to meet a stupid law about increasing bio-componants in the national fuel supply. This came about from the "bio-fuels" boondoggle a few years ago, where were all going to use gas made from grass and weeds. It never worked, but the law still stands and corn alcohol is the only way to meet it (or, attempt to do it). Unless you have a flex-fuel vehicle, it is not advised to use anything above E-10.

PRI-G is a very good stabilizer too. And, yes, draining the tank on your small equipment is a good idea. But, I've not had issues using PRI-G with winter storage in bigger lawn mowers and old cars. But I buy the pure gas for my 2 cycle engines (premixed 50:1, you can get it at places like Home Depot, in the red quart cans).

This is all from memory, so someone may come along and correct a point or two.
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mrbone
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Re: Mower Repair Question

Post by mrbone »

Looks like the coil theory is most likely correct. I always assumed a bad coil would just prevent it from starting, not reduce performance. I confirmed the air filter isn't the issue and that the flywheel key is aligned with the crankshaft. Next I tested the resistance in the coil and get about 5.25k ohms. Online consensus seems to be that once it gets over 5k ohms then it's shot. I'll buy a replacement Monday and see how it goes. Thanks!
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