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J.R., Small Engine Technician
Category: Small Engine
Satisfied Customers: 7445
Experience:  Owner of outdoor power equipment business, repairing all makes and models.
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I have a Snapper lawnmower with a 6HP Briggs. It will not start

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I have a Snapper lawnmower with a 6HP Briggs. It will not start after it gets warmed up and you stop to empty the bag. I have changed the plug, air filter, needle valve and set. done a valve job and changed the head gasket, and changed the coil. I don't know what else to do. Any answer to this?

Have you tired a new gas cap?

Customer: replied 7 years ago.
You may want to check that. The gas cap may not be venting.
Customer: replied 7 years ago.
If I try that tomorrow and it doesn't work, how do I get back to you to let you know?
Customer: replied 7 years ago.
If the mower runs fine when it is cold, How would warm gas in the tank or carb.or hot engine cause the vent in the fill cap to not allow the gas to flow properly? Don't understand.
The cap itself may not be venting. If it does not vent it will not allow gas into the carburetor.
Customer: replied 7 years ago.
I understand that if the cap doesn't vent, gas will not go into the carburetor, but why would it vent and the engine run great when it is cold and then be so hard to start if you turn it off after it warms up, to empty the bag. It will eventual start if you pull a lot, fast, otherwise you have to let the engine cool off.
I would try a gas cap and see if that helps. It may be something to do with the engine temperatures causing a vapor lock.
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