Recoil Starter kick back

[Matergrower]

I have a Weedeater brand rear tine rototiller. It has a 5 hp Briggs and Stratton horizontal engine. The problem is that the recoil starter will kick back and literally jerk the pull cord handle out of your hand. This is not an occasional thing, it happens every time the pull cord is pulled. If I'm not real quick and let the handle go it is very painful. I think I may have torn some ligaments this morning when I was not quite fast enough. This tiller is older, about 15 years, old and has had this problem since it was new. I have had other power equipment with Briggs engines both smaller and larger with recoil starters but I've never had an issue with the others. It seems that the timing is a bit off but I have no idea how to remedy this problem short of trashing this tiller and buying another.
Any suggestions are welcome. Thanks

 

[ILENGINE]

First thing to do is to check the flywheel key. Partially shears or broken will cause kickback problems.

 

[Matergrower]

First thing to do is to check the flywheel key. Partially shears or broken will cause kickback problems.

Since this engine has done this from day one out of the crate I assumed the flywheel key was undamaged. Of course, with my career being in aircraft maintenance I've learned to assume nothing. I will check the flywheel key when my hand heals from the last kickback.:frown:

 

[bertsmobile1]

The wrong plug and paricularly a gap that is way too small can also cause kick back on start as can a mistimed cam and bad valves or valve lash but the key is the most common 95% cause and ight plug gap makes up 4% of the remaining.

 

[Matergrower]

The wrong plug and paricularly a gap that is way too small can also cause kick back on start as can a mistimed cam and bad valves or valve lash but the key is the most common 95% cause and ight plug gap makes up 4% of the remaining.

Correct spark plug is installed and gapped to .030. The flywheel key was very slightly marked so I installed a new one. Afterwards the kickback is as bad as ever.

 

[Matergrower]

First thing to do is to check the flywheel key. Partially shears or broken will cause kickback problems.

The flywheel key was very slightly marked so I replaced it with a new one. I also replaced and gapped the spark plug. The kickback is still as bad as ever.

 

[Matergrower]

One thing I failed to make clear is that it kicks back (jerks the recoil cord and handle out of my hand) before fuel is even in the cylinder so pre-ignition is not the problem.