I had a Volvo P1800 for a few years that had a pair HS4 SUs. Yes they were easy to tune. I forget the name of all the parts. The trick was to get a tool from your local foreign auto parts. The tool was a pair of pipes that replaced the diaphragm damper with wires were place in the top of the at a right angle. Back off all your adjustments and line the wires up. Start the engine and tune while keeping the wires lined up. Could never find a set of needles I liked to go with the Isky cam.
Larry
