Before I do everything possible to get the head off and fit a new one, Does everyone agree that this is probably a valve issue, having fitted electronic ignition and got timing set up right, rebuilt carbs and set up right, new fuel pump and checked flow from tank. Starts and runs great, and did 500 mile round trip at the weekend ( yes 500!), which was remarkably uneventful, eating up the miles with little fuss despite not having full performance.
However, it starts to run out of power above about 3,500 and if rev high on full throttle or pull hard (especially uphill) on full throttle, after a few seconds it starts to loose power, then coughs back through the carb, giving a foul smell of half burnt fuel. When we did the carbs it was the rear one that had soot marks in it, and it's the rear cylinders that show lower compression and a quick loss of compression when tested- not sure of the figures.
Also, where best to go for a standard recondition unleaded head? - looked at Qulliers recently.
Finally, looking to make it a bit quieter with some insulation ( for those 500 mile journeys) but it has a strange resonant drone that oscillates. When doing 50 to 80 and under power, the deep drone rises and falls steadily every 3 seconds, but seems to go when you lift off the power. Never got any worse and wondered if prop shaft imbalance. All this combines with general engine clatter, a sligh wine from the diff ( reconditioned) and the tweety in e clutch - so fitting the radio was a big of a waste of time really!
Cheers
Dave