G'day Robert,
This is one question that like most things over the Internet, is difficult to diagnose.
How long does it take to oil up? Have you tried hotter Plugs? Is the Ignition strong enough to supply a good strong spark?
There are a couple of tests that need to be performed.
(1) The Compression Test, both Dry, and Wet, and these will give an insight into the condition of the Compression Rings, and the Sealing of the Valve Seats.
(2) Could be worn out Valve Guides, and or broken Valve Stem Seals. These can be checked by pulling the Rocker Covers and checking the sideways movement of the valve stems within the Valve Guides, and visually observing the Stem Seals.
(3) A Leak-down test, which the average mechanic cannot perform.
The above tests need to be performed as a minimum, but without pulling an engine and stripping it down to check the critical measurements, it is hard to say.
With the Cylinder Heads removed, one can feel the tops of the bores to see if there is any ridge, which could indicate broken rings, as the top ring constantly striking the ridge on the upward stroke, don't like hitting ridges.
Bruce.
