i used 2watch mines drop all the time 2then i realised it was just the excessive use of a heavy foot on the throttle! lol!
and also as mentioned above when goin round right hand corners and roundabouts it used 2drop as well! if it was under a quarter tank of fuel it used 2spit and splutter and nearly cut out but that was just the petrol being taken away from the pump i think? lol!