Sea Bandit, sea trials

Hi everyone, launched the "Sea Bandit" at Brightlingsea today, first trial since refit, never had a fast fishing boat before, always opted for the displacement style, so wasn't sure quite what to expect, started up the engine, a 70 hp Evinerude (ex RNLI) 2 stroke to let it warm up while I set up the electronics, vhf, f/finder & plotter and had a cuppa, it felt a bit lumpy but the technician who fitted it said that it would need a good run, so of we went, 4 knots & then 8 knots as the bouys demanded, into the deep channel so I thought I'd give it half throttle, well I wasn't expecting the result, I was doing 25 knots in what seemed a couple of seconds, there was loads of throttle left but to be honest I bottled it a bit and cut it back to around 18/20 knots, checked it all out while for around an hour and a quarter, I was pleased with the fuel consumption (12 ltrs), around 10 ltrs an hour, but it still seemed a bit lumpy at low speed, under 8 knots, a guy in the mariner said that most 2 strokes are the same, any suggestions as it is still under warranty, cheers Stevie.