Petrol Mower starting problem? I have a 3.5hp Petrol Lawn mower, which is in the region...

I have a 3.5hp Petrol Lawn mower, which is in the region of 10 years old but still works okay - when I can actually start it short causing myself an injury. The starter pull-cord will sometimes snatch hindmost and recoil so firm it almost breaks my wrist. If I am brave enough to perservere, once it does start its OK for a while, but after when I am least expecting it, following a stop to unfurnished, it does it again. I'm almost getting afraid of it now. What is cause this and is there a hurried fix, other than a latest mower?
What is wrong near my lawnmower?
Answers:    Needs a tune-up.(new spark plug,replace air filter,verbs carburetor bowl,re-set magneto gap,verbs and polish commutator.)
I want to burn wood for steam but...
testing...trialling