18 hp B&S starting problems

roper1July 27, 2010

My 18 hp twin B&S garden tractor starts easily when cold and runs great, but will not start after it has reached operating temp. If I remove the plugs and give them a quick clean with a bass brush it will start and run smooth. The plugs do not appear to be fouled when I clean them. If I leave it running it works fine with no loss of power until it runs out of fuel, and when it cools it fires right up. Any light shed on this problem is appreciated.


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It could be an ignition switch. The contacts inside the ignition switch can fall apart or break.

I've included a link to another thread about B&S starting problems.

Here is a link that might be useful: 18hp briggs & stratton starting problems

    Bookmark   July 27, 2010 at 6:47PM
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esemilio(Z5 WI)

I had a similar problem with a B&S 42A707 engine. It was the ignition coil. It would start immediately when cold and not stop unless I turned it off but once stopped it would not start again unless it cooled. Oh yeah, it would start (only the first time) if I put in "new" plugs; the second try would have the same problem.

    Bookmark   July 27, 2010 at 7:10PM
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Interesting, I just quickly browsed the site recommended above. Thing I noticed right off was the statement that a sheared or partially sheared flywheel key will "Kill" the spark which of course is not true. It will have absolutely no affect on the quality or quantity of spark, only the TIME of the spark. I am not a member so couldn't post a reply.

Hope there is better info than this.

I suggest turning off the gas 15 seconds before shutting engine off and see what happens.

Walt Conner

    Bookmark   July 27, 2010 at 7:51PM
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Well I should have added ones equipped with CDI which we don't know since the model number was not posted. The one in the post mentioned above was a 1992 which would be CDI.

Walt Conner

    Bookmark   July 27, 2010 at 8:08PM
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Thanks for the help. I will try the suggestions. Here is the engine info I forgot to include. Engine Model # 422707-1243-01.

    Bookmark   July 28, 2010 at 9:41PM
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Roper,I have a B&S twin doing the same thing. I posted it about 6 months ago and got a lot of responses.(might want to look it up). Next time it wont start when hot,check to see if it has spark. Mine does not have spark,when hot and trying to start it. After it cools down,it starts and will run(good) till out of gas.(acts like yours) I have rep;aced the coil and it made no difference,although it sounds like a bad coil. Now I know this sounds crazy,but if while trying to start it hot,if I ground one of the plugs,it will start every-time(remove ground after it starts). I found this by accident while checking to see if the cylinder had gas in it. I had removed one of the plugs and grounded it while turning the motor over,as I suspected it might be flooded .(had learned from past experience to ground the plug,as if wire is not grounded,it will ignite the gas coming out of cylinder) and it started up on just the one plug connected. I replaced the plug and the wire and it wouldn't start.(remember the engine was still hot as all this happened in about 2 minutes) I dont remember why,but I grounded the plug while trying to start it and it started. So now anytime I want to start it when its hot,I ground one of the plugs and it starts everytime. Since its works everytime,I quit worrying about why,and wondering if I am in the twilight zone of motors. Try it on yours and see if it helps.

    Bookmark   August 1, 2010 at 9:42AM
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