Lawn mower problems?

I have a Murray 22" cut 4.0 HP Spirit push mower. I was mowing the grass and it was running fine.I decided to replace the blade on it as the blade was worn out. While I had it on its side, I decided to change the oil in it as well. I cleaned out all the grass that was caked on under the deck. I put the lawn mower back on the ground and was going to try to start it as I was going to mow some more.The mower is only about 2 years old. I have only had to push the primer button 3 or 4 times and fires right up every time. Anyway, when I got ready to start the mower, I pulled the cord on it a couple of times and it locked up on me. I could turn the blade manually (hard to turn) but I turn it and free it up and pull the cord again and the same thing would happen again, it would lock up.I have done this same thing several times, it locks up I turn the blade manually and 3 pulls it locks up. Help me out, what is causing this problem.

Answers:
Several things are causing your problem.......Oil has run into the cylinder.
The Engine Safety Brake is not disengaging an is keeping the motor
from turning
Clean the spark plug and the airfilter.........then go for it!!

Other answers:
Pull the plug out and check for oil. when you had it on its side maybe some oil got into the cylinder. If so you need to drain this out and clean the plug. Let it set for a day and try again. Or try pulling the cord with the plug removed to see what comes out. Just recheck your oil level prior to starting.
Pull the plug out and check for oil. when you had it on its side maybe some oil got into the cylinder. If so you need to drain this out and clean the plug. Let it set for a day and try again. Or try pulling the cord with the plug removed to see what comes out. Just recheck your oil level prior to starting.
oil lock . pull the spark plug out . pull the cord to get oil out . clean plug .
What gary said is good.
When people turn a lawnmower on its side the oil will go everywhere - and if a valve is open it can fill up the muffler too A Very dangerous situation.
You must be precise on filling the correct amount of oil - some are a pint some are 3/4 of a quart.
If it has to much oil it will not turn over and can break easily.

Take out your spark plug and loosen (don't take off) the oil cap and crank crank crank or pull pull pull
Good Luck and let us know how it turn out in comments.
What all the above said is true. I've been repairing these things for over thirty years. Put the machine back upright, drain the oil, remove the spark plug and clean it (an old trick is to spray the tip with ether Starting fluid), put the mower over a half dozen times, add the oil to the crank, then spray a little (one small squirt)starting fluid in the engine (spark plug hole), put the plug back in, don't choke it or prime it. Pull the cord until it starts, but it will quit because the plug gets wet fouled. repeat the spraying of the tip and a little in to the spark plug hole. That should do it and it should start normally.
Jeez, EVERYONE is right... Always, when getting under the deck, raise the mower so the plug is skyward. If you do this, you will not get the oil accumulation in the cylinder and air cleaner... Makes a real mess when it takes off, and plugs up your air cleaner... Simple fix, wish you luck !
If its still locked up.. and you've made sure the cylinder is free of any oil....., make sure the flywheel brake (its let go when you hold the handle down) is actually letting go of the flywheel. Take the shroud off (4 bolts) to get a good look at it.
Might want to pull the spark plug out and clean it. Also when you try to start it do you hold down the safety handle when trying to start it. It is not recommended to turn the mower upside down while changing the blade. All the oil will flow into parts of mower where it shouldn't be. Good luck
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