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18 hp B&S starting problems

13 years ago

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.

PJ

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Comments (6)

woodsmower
13 years ago
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
esemilio
13 years ago
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.
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An excerpt from the bulletin "APSI #: 87 DATE: NOVEMBER 2012 SUBJECT: CYLINDER HEAD TORQUE CHANGE MODELS: 210000 280000 310000 330000 OHV VERTICAL SHAFT ENGINES" "Briggs and Stratton recently changed to a new design cylinder head bolt for model 210000, 310000, and 330000 OHV engines. The new bolts require a higher torque during installation. At the same time, we have modified the bolt tightening sequence to reduce the chances of head warpage at higher torque settings. To prevent confusion, use only the new tightening sequence and new torque value when servicing both older and newer designs, including the model 280000 OHV. The following procedure will replace what is currently shown in repair manual 276781 Single Cylinder OHV Air-Cooled Engines."
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Oops my mistake, tried to get as much info as I could from smarter people than myself. Could this coil problem also cause it to start with no problems other times and also to lose spark to just one plug. It started today with really no problem at all. Then after running for about 10 minutes, it would only fire on one cylinder. Thanks again.
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As walt sez--do not run the engine without the cooling shroud in place. But, to momentarily test it, to see if it is right, you can run the engine for at least 20 seconds, to check it, but no longer. And, next time you put it away for winter storage, stuff some of those perfumed clothes dryer sheets around the engine shrouding, and the carb/air filter. Mice hate the smell, and will avoid it like the plague! Use a shipping tag, or business card to set the air gap on the ignition coil to flywheel setting. Trying to set it with a feeler guage is hard to do, as the area is rounded, so the card works great.
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walt2002
13 years ago
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
walt2002
13 years ago
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
roper1
Original Author
13 years ago
Thanks for the help. I will try the suggestions. Here is the engine info I forgot to include. Engine Model # 422707-1243-01.
Thanks
PJ
ollieduke
13 years ago
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.

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