For some reason my mower backfires when I pull start it, but that usually happens between starts after the mower is hot. Now it is starting to run pretty rough and vibrate. I have already replaced the spark plug and cleaned the carberator. It seems like to me that maybe the timing is off or something. It has pretty much gone down hill since I caught a small stump a while back. I replace the original blade because it was bent. The replacement blade I bought was a universal since I was not able to find the original style. Can you please point me in the right direction on the problem. Thanks

Hi,
I would say that you did more damage than just to the blade. Sounds as if you have sheared the flywheel key (backfires) and bent the crankshaft (vibrates.) A new key will fix the ignition, but with a bent crank you can expect the carb and muffler to come loose and try to fall off at some point in the future. Other things could happen like rivets holding starter and screw holding fuel tank.
Sorry about that.
Peace,
Clarke

Thanks for your time

Hi, here is a picture of the broke flywheel key. What do you suggest as far as trying to remove this thing without damaging the threads? Do I need a flywheel puller or holder to accomplish this?

Hi,
Well Briggs does make and sell flywheel pullers that they recommend (and I necessarily have and use one.) "In the field" it is not always possible to have every needed tool, and "shortcuts" exist for those circumstances.
In this case there is one that only involves a hammer and a pair of hands. The flywheel has two distinct flat areas around its circumference. One contains the magnets used for the ignition and it off limits. The other one should be on the opposite side. It is weghted for balance even if not visible.
Tie off the flywheel brake (always best to disconnect the plug) and turn the flywheel so as to be able to strike that weighted spot sharply and directly in line with its surface (basically if the surface is vertical, then the hammer face should be also when it strikes it.)
At the same time you should have your other hand opposite this lifting (I use fingers beneath the magnets and thumb on tip of crank.) One or more sharp blows in this fashion should free the flywheel for key replacement (it will have the sheared key add some resistance to the process.)
Once removed, clear the pieces of the old key, put flywheel on the shaft turning for alignment and insert new key. Put on washer and nut and torque to 55 ft lb. Reassemble.
Please note that this is not a recommended method and will with time (repeated use) deform the taper on the inside of the flywheel that meets with the crank. Once will have little impact.
Peace,
Clarke

Ok, I will let you know how it goes. Thanks

OK I did purchase the flywheel puller from the Briggs and Stratton website and I just got it today. Now how exactly do I use it? Do I use the crankshaft nut or what, and if so none of my tools can fit between those self tapping screws.

Hi,
Good for you! Thread the flywheel nut down until the top of the nut is flush with the top of the threads. You have the puller correctly shown. Back off on the nuts above body (thread toward heads of bolts) and the nuts you have against the flywheel in the picture back upward to just below the body of the puller. Begin to tighten the self-threading bolts (has been a 3/8" socket in the past.) They must cut cut deep enough to grip reliably (5 -6 turns) without the nut touching. Once the bolts are fastened in securely, run the nuts down to the puller body with your fingers until snug and puller is flat on the nut. Now tighten one nut 1/4 turn, then the other 7/16" wrench.) Do this until flywheel pops and can be lifted; then the bolts can be taken out, puller lifted off, flywheel nut taken off and flywheel removed.
Note: the flywheel brake (safety bail) needs to be tied off for this. And note that the two nuts on the side of the puller nearest the thread-cutting ends are only there to keep the bolts from falling out of the unused puller and should never be tightened against anything.
Keyways can be cleaned and flywheel put back on crank. Line up the slots in flywheel and crank and insert key. Tighten flywheel nut to 55 ft.-lb. (safety bail no longer needs to be tied.) Reassemble and mow.
Peace,
Clarke

Well the key is finally replaced and the mower is definitely running better and of course no backfiring. Only thing is it seems to be running a little rich. I think I must have stretched the spring on the throttle. I will try adjusting it next chance I get. Thanks for all of your help and you will probably be hearing from me again in the future since my luck with this mower has not been very good.