I have a honda hrb 476c mower. It was ok last year but now coughs & stops ?

Come to start today, after several pulls it ran, but stopped after about 15 seconds. It restarts ok on first or second pull but again, coughs and splutters to a stop. I have perseverd many times, but cannot get it to run any longer than 10 to 15 seconds each time. Any ideas?
I cannot seem to find the origional manual