Your link did not work, so I have taken the liberty of fixing it.
It is essntially the same as what I said in my post to a simular set of numbered drills , but mine are available in this side of the pond.
Great minds think alike
Thanks for fixing the link.
"The bitterness of poor quality remains long after the sweetness of low price is forgotten". --Benjamin Franklin
"Don't argue with an idiot, they will drag you down to their level and beat you with experience". --Mark Twain http://www.campbellmechanical.com
I had a similar problem a few years back. Several techs before me tried everything and still could not correct the problem. I put my gauges on and immediately could see there was a restriction. Guys before me pulled the piston and checked it and it appeared fine. I pulled the piston and it wasn't plugged but the orifice looked too small for the size piston. I pulled out my handy drill index to check the piston and sure enough the orifice was too small. It was the correct piston but somehow copper had deposited itself in the piston orifice. I used my drill and chipped out the copper and put the piston back in and it worked great after that.
You really need to measure the piston orifice to make sure copper hasn't reduced the orifice size through some type of electrolysis. You'll need a drill index that measures orifice sizes.
That's very interesting, I wouldn't have considered that.....