Hi wce, Hru19r is a gcv, an engine which I am not a major fan of. I would wager either marginally stuck valve through fuel varnish or carbon, or slightly off valve clearances.
They seem t be so much more finicky and pedantic than a gxv - plus they are hard to decarbonise since you have to split the case. All you can really do is take the filter out and spray something like threebond carbon clean spray down it whilst revving it hard
The decks are great though, I have a V40 Victa engined one
