my mountfield hp470 "chugs", more than runs smoothly?

unscrew the the foam filter holder, check for dirt or water.
If the filter is greasy soak it overnight in warm water and fairy liquid, then dry naturally.
Change the spark plug, or unscrew it and clean the contacts.
However if it hs been stored on an angle, you will have oil in the main cylinder... if you do, its a fix that costs more than the mower is worth.
I have the same mower, and the same issue.

carl
May 2008