Inconsistent Kreepy Krauly Performance

[Novice Pommie Pool keeper]

Just like every English sports team, my kreepy krauly performs in a very haphazzard way. At times, it motors along fine and then seems to slowly run out of steam! There are no holes in the hose, i have just bought a new filter plate (the old one was cracked) and there are no blockages? Any ideas would be greatly appreciated!!