How can I fix my Honda ohc rotavator?

I have a Honda 4hp four stroke ohc rotavator, 7 yrs old which starts ok ,runs on tickover ok, but when in action it tends to stall occasionally and cut out.It has only just started doing this. When it seems to be going to stall, if I release the drive and let it tick over, it seems to run ok for a while.Is this just dirt in the fuel line or something else?
Help would be most welcome