Hi Norm and all
The mower is pretty new but has the air filter been replaced with an after market one ? is it foam or paper ? These new engines are set to run so lean that any alteration to air flow will have a big impact. I went to clarke rubber and got some offcuts of foam which felt and looked like it would do the job for air filters but gave the exact running issue of the mower you have Norm. I would suggest trying a genuine replacement air filter, if that isn't the answer at least they will have a spare.
Cheers
wce
