hi i have a z8 2017 model and recently went to an off road centre , plent of mud and water but nothing harsh
anyway on the way home on the motorway as soon as i was reaching 59mph the Buggie started to splutter and slow until i dropped below that speed , it has only ever done it from this off road event as i used to be able to reach 70mph
this is currently with my dealer who have plugged a diagnostic machine in and it is not showing any faults  , they have checked connections , wires etc and cant find anything
has anyone had anything similar to this fault ? any ideas would be welcome

[2015 Z Force 800 53/Trail EPS]

Have them check the fuel pressure and volume. Also the tank check valves fail as in either stick open or shut. If shut, it can't get the air it needs to displace the fuel it takes out making the pump pull against a vacuum...which reduces its pressure and volume especially at higher speeds and usage times. at lower speeds and lower usage this problem may not show up. Mine failed open and would push fuel up the tube and into the frame where they placed the end of the vent. Also, the fuel filter...it may be plugging with dirt or even moisture preventing higher flow rates.

thanks for that will forward your reply