I have a very good hongda gx240 (8hp) with an interpump ws151 + gearbox, does 150 bar @ 15 litres per minute, excellent condition and just serviced, ideal for mounting on a van, comes with 15 metre hose and lance, lots of new parts including unloader valve, air filter, trigger gun, all brand new parts, runs mint, not got round to putting it on a frame yet so would take £400 as it is, it's suprisingly powerfull for a 150 bar machine due to the fact that it runs at 15 litres, if I put this on a trolley I would expect it to bring around the £500 mark on ebay being in excellent condition and serviced. let me know if tyour interested, I am based in Wigan, north West... as for reducing the power in a 21 litre machine a simple answer would be to not buy it as opposed to tampering about with it, just go for a 15 litre machine... like the 1 i ahve for sale...