Thanks for the replies chaps.
It's a homebuilt (RV-4) on a permit to fly and my inspector is happy for me to do the checks myself. I'm not a mechanic, just an engineer, and have been helping out with 50 hours etc. for over 20 years and am very carefull with props and pressure in the pots.
As SNS3Guppy says, I wouldn't pull a pot based on one test. The last test was done cold for various reasons and the pick-up strainer and filter elements closely examined (both were clean). The engine runs smooth and achieves it's "book figures" for climb rate - 1400 ft/min at gross and 2000 ft/min solo.I would expect a .060 orifice, at over twice the area to have a much lower pressure drop and give results nearer to 80 as a result.
Just wondered if anyone had compared results with both orifices