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Lawn Boy 8072 mower wont run

3 years ago

last modified: 3 years ago

My Lawn Boy 8072 wont run. It will start after numerous attempts , but dies after a few seconds. This happened suddenly. Before that, when it DID run, it would speed up and then slow down. constantly.

New spark plug, I removed carburetor, needle valve is clean, float is clean, I sprayed throttle valve, it is free,new air filter. I tightened the mixture screw until seated, then backed out 1.5 turns. and made several .125 turn adjustments. No avail. I tested the dead mans swithch with a VOM. It operates correctly (open when handle depressed).

I suspect trouble with the throttle valve spring (governor?). If I'm quick enough, and hold the air vane, engine will continue to run, and at a steady speed. I thought the spring was strong enough (checked when I removed carb). How difficult is it to replace? I watched a video this morning, where the poster said to keep the air filter box attached to the carb, as it "is a pain" to re-connect the throttle spring.

Why would a spring become weak suddenly? I had a similar issue with my lawn boy snow thrower, but the governor spring actually broke. It was a lot easier to replace (regular spring, one end hooks into one hole, the other into another hole)

Ideas?

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Comments (5)

tom10418
Original Author
3 years ago
last modified: 3 years ago
Update: I turned what looked like an adjuster wheel where one end of the spring connects. This seems to have increased tension, and now I can get the mower to keep running without my having to run and grab the air vane. I'll order a new spring anyway. And don't you know, I ran over the air filter cover with mower yesterday, so I have to get a new one of those!

Problem that still exists: How do I adjust the mixture? It takes many attempts after priming to get engine started. Am I flooding the engine (i.e. do I need to close needle valve?)
rasims
3 years ago
last modified: 3 years ago
Here is a link to the manual for your mower. Your engine should be an F-140.

https://lookup3.toro.com/ttcGateway/Acrobat/manuals/lball14.pdf

Sounds like a lean condition due to the plastic carb flange warping and causing an air leak. Those plastic carbs are notorious for that. Check it with a straight edge and a good light. If it’s warped you can file it flat again and install a new gasket and hopefully be back to a good running condition.

Don’t forget to check for leaky crank seals while you have it on the workbench.
tom10418 thanked rasims
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tom10418
Original Author
3 years ago
last modified: 3 years ago
rasims (or others): I removed the carb, cleaned it, checked float position as per instructions you gave me. All OK. There's no warping on carb flange.

Mower will run for a short time, but after five or ten minutes, it will start to rev up and down, and then stop. Question: Will lack of air cleaner cover do this (too much air-> lean mixture)? I have the foam filter in place only. But, it was doing same thing before I broke the air filter cover (I'm awaiting a new one.) I adjusted the mixture as per instructions (seat, open two turns, etc.) No matter what I do, the rpms rev up and down.

Should I clean the jets? Could that be a problem? I think one is on the side of the body, and another under the fine cylindrical metal filter screen? Is this correct?
tom10418
Original Author
3 years ago
Problem solved!

I pulled the carburetor again, and this time I cleaned the jet (seat) which accepts needle valve activated by the float.

Inside I found a "screen". I figured I would clean said "screen". Lo and behold, I discovered that the "screen" was a clump of debris, blocking the fuel inlet at the carburetor body.

No wonder it wouldn't run. Carburetor was starved for fuel!

rasims: The carb manual you posted helped a lot. I tweaked the mixture adjustment, and the mower starts on the first pull when engine is hot. Thank you!!!!!

The thought of buying a new mower now..... :(
rasims
3 years ago
Glad you got it figured out!
tom10418 thanked rasims

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