Pulsing pressure washer / foam cannon

[Hereward]

I bought a new "PA LS3" foam cannon for my Karcher K7 Compact pressure washer which makes my K7 motor pulse (cut in and out constantly) when in operation. If I switch back to the standard Karcher foam cannon the motor/flow is fine.

Water flow rate seems ok - the pressurised Karcher cannon delivers ~10 litres per minute.

I thought the K7 was a decent machine but is it not powerful enough for the new cannon? The new PA cannon has an internal 1.25mm valve - can that be swapped out?

Thanks for any advice.