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I filled the 3.5HP B&S up with a full tank of unleaded today, and mowed the back and front lawns withough a hitch, so I finished, took the grass collection bag off, and tried to fire it up, to get rid of the remaining loose bits of grass under the mower, but it just would not fire up!

I tried it for ages with the throttle on MIN because it was warm, so then I put it on CHOKE, and tried more, nothing, back to MIN, tried again, NOTHING!!

Every few pulls it would pull the cord back and almost dislocate my elbow, but I don't know if that means anything, probably not.

Please help guys! :frown:

The engine only has 4.5 hours on it!

Classic symtom of a sheared flywheel key.

And is that bad ? Hard to fix/expencive ? :frown:

That depends on how mechanicly you are inclined. The key is just a couple of dollars. To replace, you will need to remove the engine top cover and the flywheel.

It's over the time limit for the warrenty :frown:

I've changed the oil in a car before, so that is about my mechanical knowledge level...

Would I be able to do it ?

jmurray01 said:

...
Would I be able to do it ?

Click to expand...

If thats your problem...
Simple easy to do ... they are all similar to this youtube clip... YouTube - How to replace a sheared flywheel key on a Briggs & Stratton walk behind lawn mower
Give it a watch... Impact wrench is also handy to remove the crankshaft nut...
You should be able to do it... :smile:KennyV

I've just been thinking though...

1) Would a small stone (about the size of driveway gravel) be enough to shear the Flywheel Key ?
2) Why did the engine keep running fine after hitting the stone, instead of stalling immediately ?

My friend says that if the engine kept running after the "collision" with the stone, it can't be the key, as that would cause it to stall straight away.

He thinks it is the "Cold Timing Advance" stuck on, but doesn't know how to fix it...

Do you guys!?

How new is the mower ???

Some newer engines have a auto shut off if the oil is low also check the deck to see if something wrapped around the blades and caused it to bind

The mower is a 2011 model.

Could somebody confirm that it couldn't be the Flywheel Key if the engine kept running after hitting the stone ?

The only way to confirm is to remove the flywheel and check the key. BTW, if you need one you can get them at Home Depot they come two in a pack. It does sound like the key. It may have finally moved when the motor was shut down.

Right. I've ordered Flywheel Keys from eBay, so when they come I guess I'll remove the flywheel and check.