Outdoor Power Equipment and Small Engines - Yard Machine 12.5 B&S will not start

Hi everyone. First, sorry for my English.

I need some help for my Yard Machine 1 year old with 12.5 hp B&S engine cut mower that has been parked in my garage for over 6 months. I ran it dry over 3 hours and then it wouldn't start after refilling the new gas that I just bought from the gas station...although the spark plug in my lawn mower has a good fire in the aluminum head. (I try before turn on the key)

When I trying to start the machine I did following:
I'm pressing the clutch pedal down all the way, and the blade engagement handle is hitting back the switch all the way while I try to start it.

Any suggestions on where to start next ? Thanks and God bless!

Try a couple teaspoons of gas directly into the cylinder through the spark plug hole. If the engine fires and runs for a few seconds, then dies, you would have a fuel supply problem and likely need to clean the carb out. As some ports are very tiny, you would need to inspect the carb very carefully.

Does the engine spin (crank) over? If not, do you get any noise, whatsoever, with the key? Did you run it dry this year or last season? Was the fuel stabilized for storage?

Thanks again ...

Today I Try a couple teaspoons of gas directly into the cylinder through the spark plug hole as your idea, but the engine still not fire !

I recharged new battery, replaced new gas ... what I will continue then ?

The engine spins well when I turn on the key to start It.
The machine ran very good at any speed last season.
The fuel that I bought form the gas station was stabilized for storage.

Is the engine full of oil? Does it seem to spin faster than you remember it spinning before? What if you turn it by hand (put your hand on the round screen on top of the engine and turn it). Do you feel it get hard to turn, then easy, then hard, etc... or does it turn really easy the whole time?

You are really Pro Cheese ... I think It's not very far from the target !

* The engine full of oil (I didn't touch the oil from last year until now.
Because I see it seems good ...!? )

* The engine seems spinning normal like last season...

* It really gets hard to turn by hand ! ... then easy... then hard...!!!
( I couldn't rotate it the whole time ! )

What must I do next step ? Please ...

Ok, it sounds like you have compression. I was beginning to think you had a broken connecting rod, but not anymore. Just to be sure, remove the spark plug, put your thumb over the plug hole with light pressure and spin the engine with the starter. Does the compression from the engine blow your thumb off the hole?

If so, you have compression. The next step would be making sure you have good spark. You said you have good spark. Did you see this spark with your own eyes? If so, then it's probably a fuel related problem, and I would suggest taking the bowl off the carb and see what it looks like. You might just have water in it, or it might be full of crud. You'll know when you get the bowl off.

Thanks again ...

Today I did following your suggestions:

I put my thumb over the plug hole and spin the engine with starter, I feel the compression from the engine blow my thumb off the hole. I replaced a new spark plug (the spark plug for starting) and I replaced once more time the new fuel after remove the bowl off carb and cleaned it up.

I restarted the machine ... nothing changed !!???

What must I do next ? Please !

I know you have a new spark plug, but can you see the spark while checking to see if the spark plug is firing?

The spark plug is firing well while I checking it Before restarting the machine. I known do that when repaired for my motorcycle long time ago.

I'm sure the problem not came from neither the spark plug & the fuel, but I don't know why the machine didn't run !!???

The engine has good fire, good fuel, good compression ...

Any suggestions on where to start next ? Thanks and God bless!

Was there fuel in the bowl when you removed it?

If you have fuel, air, fire, and compression, it should run. I like Azis's question: was there fuel in the bowl when you removed it? If not, it may still be a fuel delivery problem. Does the spark plug look wet at the electrode?

Two things that need to be better diagnosed! The ignition strength and the compression. I know you have spark (so it seems) but do you have sufficient spark? An inline spark tester would be best to determine if you have good, sufficient spark. Apparently you have compression but I wonder if you have sufficient compression or possibly a valve train related issue. Ideally, you should perform a combustion chamber leak-down test to check the condition of each valves ability to seal well along with the ability of the piston rings to seal and also the condition of the head gasket. A leak-down can help you pinpoint any combustion chamber trouble, if any.

There was full of fuel when I removed the bowl. There was only fuel, no water in it at all !

the spark plug looks dry at the electrode.

Thanks again.

Try dumping a tablespoon or so of gas into the intake and try to start it. See if it cranks up for a second. I'm just trying to think of what could be wrong with a 1 year old mower that was only run dry before storage. I would suggest warranty, but I think you probably have a fuel problem, which likely won't be covered by warranty.