Old Yammie F100 is a lardy bit of kit at 164kg. I've read the carbs on these mid-sized 4-strokes are quite picky regards fuel. Best to disconnect fuel supply after a run and open choke until it stops.
Can't fault the Delta. Deep V hull, very capable boats. If tube condition is as you say, then easily £7k.
Worth adding to the mix...
Delta Rib 5.5m | RIB Boat and Engine Sales | Galloway Marine Northern Ireland