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Sears riding mower not running right

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05-18-2008 17:05:01

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Hi, I have this 80's model sears craftsman 38" 12 hp B&S engine with overhead valve. It has the square valve cover on the front which of course drips oil on the exhaust and muffler below coming out the front.

Anyway, it is the old mower that I use to mow around the ditch and RR tracks.

It starts and runs smooth and great for about 20 or 30 minutes when it starts sputtering and missing and then finally quits after 2 or 3 minutes. Then it won't hardly turn over. Let it cool down for an hour or the next day and it will start right up and do the same for another 20 or 30 minutes.

I've had the carb rebuilt and it is ok. Adjusting the jet when it is sputtering doesn't help. I can take the gas cap off and still no help. I can remove the needle from the bottom of the carb and gas runs out.

Any ideas? Thanks.

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05-19-2008 11:47:38

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Re: Sears riding mower not running right in reply to bc, 05-18-2008 17:05:01

Thanks so far. I always kinda thought it was a valve problem but that may not account for it being hard to turn over unless it kinda sticks closed. I kinda attributed that to the old battery not very strong. First try it would barely turn over 1 stroke. Next try it may make 2 or 3 strokes, etc., so I couldn't rule out the piston getting hot except the hard cranking is intermittant. It may be a combination of things with an old engine. I see now a bad coil could cause this but not necessarily the hard cranking. Not sure it was totally a heat related issue cause it gets plenty hot in the first few minutes and still goes. I looked to pull the plug yesterday but I didn't see it and it was too hot to go feeling for it. The plug must be hidden up under the cowling or by the exhaust. I'll price a magnatron coil since it is still worth having around if it is a cheap fix. If it is a piston/cylinder issue then I'll just settle for mowing a part at a time. Anything I can add to the oil or gas to help get the carbon buildup off of a valve?

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Goose

05-19-2008 07:14:35

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Re: Sears riding mower not running right in reply to bc, 05-18-2008 17:05:01

Same thing happened to me on a JD 111 with a 11 hp Briggs engine. I finally faced the fact that after 20 years it was just flat wore out.

I went to JD and asked the parts man about a short block. He said, "You don't even want to know what JD wants for a short block. I can sell you a brand new complete 12 hp B&S that will bolt right on for $419".

I went for it, and he was right. It did bolt right in. And really woke that mower up!

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Kentb of SWMO

05-19-2008 06:34:33

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Re: Sears riding mower not running right in reply to bc, 05-18-2008 17:05:01

NO CONDENSER on this engine. Coil has electronicaly trigger built in. You need to replace the MAGNETRON coil. This start happening on most Magnetron coils after about 10 years of age.

Kent

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craftsman

05-19-2008 05:42:25

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Re: Sears riding mower not running right in reply to bc, 05-18-2008 17:05:01

sounds like you need a new coil. But if this engin has pionts you might want to replace the points & condenser also.----craftsman

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circus

05-19-2008 03:09:50

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Re: Sears riding mower not running right in reply to bc, 05-18-2008 17:05:01

Remove the engine cowl and clean the cooling fins.

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Bob/Ont

05-19-2008 07:32:50

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Re: Sears riding mower not running right in reply to circus, 05-19-2008 03:09:50

"Then it will hardly turn over"
Sounds to me like it's overheating and seizing up the piston skirt in the cyl bore.
Later Bob

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IH2444

05-18-2008 20:08:27

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Re: Sears riding mower not running right in reply to bc, 05-18-2008 17:05:01

Valve sticking or the coil getting hot . Or I have even seen a condenser cause this problem. When it wuits is the spark plug wet or dry ?
Ans also after quitting does it seem to have good compression and spark ?

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Maark

05-18-2008 17:13:46

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Re: Sears riding mower not running right in reply to bc, 05-18-2008 17:05:01

your exhaust valve has carbon build-up on the valve stem. As your engine gets hot, the stem expands, the build-up of carbon on the stem causes the valve to stick when hot. Remove the valve and use some emery cloth on the stem. Replace and mow.

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RobMD

05-18-2008 17:10:13

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Re: Sears riding mower not running right in reply to bc, 05-18-2008 17:05:01

Plug? Fuel filter anywhere? Wonder what kind of ignition it has - maybe the condenser is going bad if it has points ignition.

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