[Cliff perkins]

My pressure washer keeps going up and down on power any ideas why this is anybody.its a petrol honda with a interpump pump.

[ducky]

does it suck its own water or from a barrel 

[Cliff perkins]

Sucks or from hose had new valves fitted about 3 months ago in pump.
Starts of 200 bar then pull trigger goes down to 100 bar then let go back up to 200 bar

[Roger Oakley]

When did it have a real good service as in engine &n pump?

You might have a valve gone, but could be pulling in air on the suction hose also.
How old is the machine, and roughly how many hours has it done?

[BDCS]

Does any water come out of the by pass when the triggers is open ? Come on answer the questions 

[Cliff perkins]

Less than year old done about 60 hours max not, been serviced yet but had new seals on pump about 3 months ago.

[Cliff perkins]

No water comes out bypass when open.i take it you mean the pressure release valve

[Roger Oakley]

Less than year old done about 60 hours max not, been serviced yet but had new seals on pump about 3 months ago.

To start with do an oil change on the engine and pump, 60 hours is just over run-in time for a Honda engine. Why the need to change the seals with so little hours? did you have a problem?
You said new valves in earlier post so is it valves or seals you have had changed?

[BDCS]

The point I was making was that if water comes out of the bypass line while the trigger is open then the unloader is leaking by which, if the pump is ok could be the cause of the pressure loss.

[Matt Gibson]

I had the same problem. Bit of grit was stuck under one of the valva caps. Holdin the valve open occasionally.

[Cliff perkins]

I had the same problem. Bit of grit was stuck under one of the valva caps. Holdin the valve open occasionally.

Would you adam n eve it was a silly hoselock conecter that was sucking in a small amount of air causing it to hunt up n down .
Id never of found that out :