Yeah i test no higher than like 7 or 8 on the gauge. Have you blanked one side and left the other open and put a test on to see if you're losing anything through the centre seal? You must do this test in 'both directions' too so: blank the left side and test whilst the right side is open and vice versa. If you test whilst both sides are blanked you will eventually pressurise the whole engine through the centre seal (if its leaking) and it will appear to be perfectly airtight. Though the tell tale sign of something being wrong is when you take the carb blank out of the side you aren't pumping up and find it gets forcibly blown out by the pressure behind it.
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After years of moaning about immigrants now i am one...