Lawn tractor engine question

Zachary Hoyt · May 16, 2011

We have an old Mastercut 12/38 lawn tractor with a B&S engine that we were given about 7 years ago because the drive belt kept jumping off, which I found was because the bolt that holds up the front end of the transmission had fallen out. It has done pretty well all this time, but this year when I went to start it for the first time it seemed to be backfiring out through the carburetor. It has spark, and when I crank it for a bit the spark plug gets wet, so it seems to be getting fuel. I am wondering if I have some kind of timing or valve issue, or if something else is wrong. I do not have any understanding of how small engines work, if they have timing gears or some other mechanism. I'm trying to figure out if it is repairable or worth repairing or if we need to get a different engine. Thank you very much for any advice.
Zach

circus · May 16, 2011

Sounds like the flywheel key is damaged. Common on push mowers when they hit rocks stopping the engine but not the flywheel.

Jim in Ma. · May 16, 2011

He said it's a rider - I don't think that is the problem.
At that age, I would try to find anotherlike it ro make one good one.

Gene Dotson · May 16, 2011

Sounds like a stuck intake valve.

teddy52food · May 16, 2011

Just try a new plug. Timing doesn't change when setting.

ericlb · May 16, 2011

if it has compression, it just needs a tune up, probably just a new plug, from personal experience, due to the extream poor quality and short life of the new riders, whatever you need to do to get that old mower going is well worth it, after my last new lawn rider a 2009, ill never buy another, it was replaced last year with a 1949 farmall cub, much better

old · May 16, 2011

I play with old mowers all the time, shoot I still have one to unload and picking up one later today but any how. I would start with a new plug or at least clean the one you have real good. Next I would check the carb a back fire can be a lean problem and now you have probably choked it and fouled the plug out with gas and maybe even water so if that carb has a float bowl pull it off and make sure it does not have a lot of water in it. Could also be a sticking valve but you would probably feel that or hear it. It could also be a shear key at the flywheel but not as likely as the rest unless it back fired real hard at one time and that can shear one

rustred · May 16, 2011

i am quite sure it would be the flywheel key is sheared. any sudden engine stop like hitting a root or rock causes this . pull the top cover and flywheel nut and check. small engines or big engines all the same principle. yes it has timing gears. a backfire is caused by timing not the carb. parts are available at small engine repair shops.

Greenday · May 16, 2011

Rotten gAS

toadady · May 16, 2011

i vote all the above,

but i did however have one that was backfireing through the carb, pulled the flywheel only to discover the key was fine, put a new plug and fresh fuel , fired right up

Wayne in MN · May 16, 2011

You could try squirting some engine oil into the cylinder to restore compression.
Then try a fresh spark plug and fresh gasoline. Makes all the difference in the world!!

JK-NY · May 16, 2011

As mentioned, try a new plug,fresh gas, give it a little shot of starting fluid in plug hole to help it get going. Also check your air cleaner -try starting with it removed. A dirty/restricted air filter may cause your flooding and wet plug.

usetob · May 17, 2011

stuck valve

Lawn tractor engine question

Zachary Hoyt

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circus

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Jim in Ma.

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Gene Dotson

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teddy52food

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ericlb

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old

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rustred

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Greenday

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toadady

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Wayne in MN

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JK-NY

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usetob

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