Was running, hit a rock and now it won't start. grass was wet too

check and clean under deck --wet grass -to slow a speed - grass to thick/to high improper hook up of bag

if you think it is a valve problem briggs and stratton website has a page that gives all the specs. for intake and exhaust vale setting. you will need to know your engine size and model number.

your belt is slipping. Have your dealer fix it.

Raise your blade up,it's bottoming out.

Blades cut the grass and blow air like a fan. The clippings should flow along with the air out into the yard or into the bag. That only works if the bag acts like a filter and catches the clippings but lets the air out to be replaced by more air and more clippings until the bag is full of clippings.
The most likely problem is that your bag does not let the air out. Cutting wet grass will coat the inside like green paint. When dry, it's like the underside of your mower.
Check the inside. You might need to scrape and/or flush from the outside in. Can yours be turned inside out"? That would be the best case.
When clean and dry, it should work.
Didn't mention the easiest fix: to take out the hand-ful of clipping blocking the path to the bad: since you already checked that.

Make sure your blades are not upside down, and your drive is properly adjusted.

well if you READ your owners manual its tell u how to reset it or fix it...

Hi, you are correct, the key will be sheered. Remove the top shroud and flywheel nut, then while pulling upwards on the flywheel have someone strike downwards on the crankshaft with a hammer and brass drift. Do not use a steel drift as it will damage the crankshaft. Hope this helps, regards Phil.

Hello,

The reason the blade slows down when the grass gets thick is simply because the mechanism operating the blade is weak and cannot move fast when on thick grass.

I suggest you troubleshoot the mower. After that, the blade should work fine when the grass gets thick.

Also, some mowers normally gets slow when grass gets thick, so after troubleshooting, if the mower does the same, then you already know it has to be slow when trying to cut thick grasses.

Take care

13 to 15 amps electric or battery operated mower may runs slow when cutting thick grass. also recommended not to cut grass when it's wet & need very sharp blade to do the lawn. may overloading it, cutting grass too thick also draws too much power. check house breaker first.