Small Engines (Lawn Mowers, etc.): Lawn Mower Wont hot start, bolt torque, engine bolts

Question
Tightened the screws to the fuel pump Cover. Tightened both airfilter screws. Ran Mower for 1 hour. Turned mower off and immediatly tried to restart. Started O.K. Let mower sit for 10 minutes. Mower hesitated but did start on second turn of the key. Let mower sit for additional 10 minutes. Had to engage choke in order to start mower. Seems to be some definite improvement! Yesterday was a cool day in my neck of the woods, will continue to monitor. May not get another hot day until Spring.
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Question -
No Electric Fuel Shut off present. A general inspection of the carbureter revealsed a small square box where the fuel hose attaches to the carbureter. The box is covered with a square plate held in place by 4 screws. These screws are not fully tightened. No sign of fuel leakage. I did not adjust tightness. I cannot find any loose bolts or screws on any part of the engine. Air filter screws were not tightened completely down, but air filter had a snug seal.
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How can I tell?

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I have a B&S Twin Valve 18 HP Engine.
The engine will not hot start. The engine will start Immediately upon shutdown, but will not sart 2 minutes later. I have replaced the coil, plugs, and checked for general tighness of engine bolts etc...
Answer -
Does your engine have an electric fuel shut-off solenoid on the carburetor?

Let me know.
Eric
Answer -
You will see a wire or 2 leading to the carburetor.  Have you checked the head bolt torque and intake gaskets for leakage?  It's pretty rare for a Briggs to vibrate the head bolts loose but it can happen.

Let me know what you find.
Eric
Answer -
That's the fuel pump.  Re-check the screw and check the vaccumm line that runs to the engine...not the gas line from the fuel filter but the other fuel pump line.  It's possible that the line ends may be not be sealing when the engine warms up...the rubber could be expanding with heat from the engine.

Let me know what you find.
Eric

Answer
Tha valve breather can also cause the fuel pump not to function.  Sometimes the vavle breather valve sticks as the engine ages.  Cleaning the valve breather with carb cleaner will usually solve a sticky valve breather flapper valve.

Let me know how it goes.
Eric