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B&S won't start


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05-06-08, 12:06 PM   #1  
B&S won't start

I have a B&S 17.5 hp in a riding lawn mower. The engine is 8-10 years old and has never had a problem. Today it started, ran for 3-4 seconds and quit. It will not restart. The gas is new. I tried using a starting fluid but the engine will not fire.

The carburator is getting gas and both plugs have spark. I don't know how to verify that the spark is adequate. Starter crank speed is normal.

I removed the air filter and cranked the engine. There seems to be a lot of fuel blowback from the carburator. I don't know if this is normal or an indication of a valve problem.

If it's a valve problem I'll probably scrap the mower, if it's ignition I'll probably try to fix it. Any suggestions on how to eliminate one or the other?

 
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05-06-08, 03:04 PM   #2  
Excessive blow back within the carb in most cases is valve related. Can you post the model and type numbers off this engine ?

 
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05-07-08, 06:48 AM   #3  
The engine is a model 42A707, Type 2238E1.

I cranked the engine with my finger over the spark plug hole. I can feel some compression but I don't know if it's enough.

 
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05-07-08, 07:56 PM   #4  
Well, Remove the plugs then one at a time put them in the plug wire boot then hold the hex part of the plug to any part of the head away from the plug hole. Then crank the engine over and see if you have a crisp darker shade of blue spark jumping across the tip of the plug, If so nothing is wrong there.

Check with your local chain auto parts stores (Autozone/Advance) and see if they have a compression tester in their "loan-a-tool" program, You really need to get some compression numbers to properly diagnose a valve issue.

Good Luck

 
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05-08-08, 06:36 AM   #5  
Thanks for the reply 31YTech -

I checked the spark and compression. Both were OK except the spark was bright, light blue. When I checked the compression I noticed that there was no gas in one cylinder and very little in the other.
I blew out the carburator with some compressed air and the engine started immediately. I had replaced the air filter and pre filter a couple of weeks ago and I suspect I dropped a chunk of debris into the carb. I think the air blew it out.

 
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