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I initially posted on the SNAPPER forum, But I would like some help from B&S engine experts.
Snapper Model 7800928 with a Briggs and Stratton engine Model No. t5vVTHXN - - - My grandson was mowing the grass for me while I was not home. My daughter was in the front yard and heard a loud "BANG" like a gunshot in the backyard. She ran around to the backyard to see that my grandson was okay. My grandson said the engine started running rough and then the bang happened and the engine stopped. They smelled gas, so they put away the push mower and started using the riding mower. When I checked it out a couple of months later, I determined that it had a good spark, that the crankshaft is not bent, that the air filter is clean and that the shear pin is good. I had to use some starting fluid to crank it and it ran rough for about five minutes until I cut it off. I cleaned the carburetor and reinstalled it, but the mower still ran rough. So, I decided to replace the carburetor and purchased an Chinese knock-of from AMAZON and when I installed it the engine hydrolocked. I returned it to AMAZON and purchased a Briggs & Stratton 591137 Carburetor (Replaces 590948) from AMAZON last Nov. I installed it and the mower still ran rough for a few minutes until I cut it off.. Now spring is here and I decided to check out the mower. I pulled the rope a few times and nothing happened so I checked the gas and found that the tank was empty. I put about a quarter of a tank of gas in the mower and pulled the rope and the engine was already hydrolocked. I removed the carburetor and inspected the needle and seat and the float and everything looks good and is clean. It seems that it would take more than just a poorly seated needle and seat valve to hydrolock the engine in less than a minute. I reinstalled the carburetor and put some gas in the tank and let the mower sit for a four hours and then pulled the rope several times. The engine would not start, but it was not hydrolocked. I waited about two minutes and pulled the rope and the engine was hydrolocked again. Am I doing something wrong? What could cause two new carburetors to hydrolock the engine?
Any insight would be greatly appreciated. THANKS!!

You probably have a broken ring and all of the fuel that was in the tank is now in the crankcase .
Drain the sump and see what comes out .
Briggs push mower engines are easy to repair and parts are cheap.
Don't continue to start the engine as you will just be making any internal damage worse .

bertsmobile1 said:

You probably have a broken ring and all of the fuel that was in the tank is now in the crankcase .
Drain the sump and see what comes out .
Briggs push mower engines are easy to repair and parts are cheap.
Don't continue to start the engine as you will just be making any internal damage worse .

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Can a broken ring cause the carburetor to dump gas into the cylinder when the engine is not running? At least once, the engine hydrolocked within seconds of filling the gas tank, the first time I puled the rope, the cylinder was already full of gasoline. Thanks.

No
But cranking a hydro locked engine does cause rings to break and head gaskets to blow out.
It takes a lot less fuel to hydrolock an engine than most think
For the sake of keeping it simple,
a 200 cc engine with a 10:1 compression ratio will have a combustion with an approximate volume of 20 cc
So 20 cc of fuel will hydro lock that engine
Doesn't take long for 4 teaspoons of fuel to run into the engine.

NORMKENN said:

Can a broken ring cause the carburetor to dump gas into the cylinder when the engine is not running? At least once, the engine hydrolocked within seconds of filling the gas tank, the first time I puled the rope, the cylinder was already full of gasoline. Thanks.

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carburetor needle isn't sealing, clean and rebuild or replace the carb.

After fixing the original problem, I find it prudent to add a gas shut-off valve in the gas line before the carb, for peace of mind.

7394 said:

After fixing the original problem, I find it prudent to add a gas shut-off valve in the gas line before the carb, for peace of mind.

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On every mower engine if possible. Fuel filter would be nice too.

slomo

Scrubcadet10 said:

carburetor needle isn't sealing, clean and rebuild or replace the carb.

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What he said. Get the carb fixed first.

slomo

Is this an OHV engine? Check the oil level if needle valve is leaking you will be overfull.

It is amazing what pulling a "dipstick" will tell!! and check the forms(Air Force Crew Chief)
Usually the fist thing I do on anything!!

mmoffitt said:

It is amazing what pulling a "dipstick" will tell!! and check the forms(Air Force Crew Chief)
Usually the fist thing I do on anything!!

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speaking of dipstick!

my old 10hp snapper hydrolocked once. I hadn't started it in about a week. Electric starter wouldn't turn the engine over so I put the battery charger on it. Hmmm....acts like the battery isn't dead.
So I pulled the dipstick andit had about a pint of "extra" oil. I had forgotten to close the inline fuel valve. First I removed the spark plug, then cleaned the needle and seat, then changed the oil and then reinstalled the spark plug. it started right up and ran fine

By the Model provided it has over head lifters. Put your old carb back on and adjust the lifters. Make sure they are getting good lift that the cam is not worn. Happed to mine. Couldnt hardly pull the rope it was so hard.

Old craftsman hydrolocked on me long ago, I removed the spark plug & hit the key, gas shot out like crap thru as goose.

I changed the oil a couple times after I got the piece of crud outta the carbs' needle valve, & added a shutoff petcock.

Most people will run the engine in a flooding condition and rely on a shutoff to kill the motor. Basically not fixing the needle.

slomo