For Dave and Phil -- 2 of the biggest differences is that the Stromberg uses a rubber seal between the piston and the upper chamber while the SU does not (relying on a close fit between the piston and chamber) -- and the other -- the SU relies on a threaded system to raise (leaner) or lower (richer) the jet (relative to the metering needle) while the Stromberg needs special "press" tools to lower the jet from the top--or raise the jet from the bottom. Different profile needles determine the running characteristics of the mixture. SU's are measured every 1/8 inch. I don't know how Stromberg needles are measured. I have an SU reference book with hundreds, if not thousands, of needles listed with each showing every measurement. I'm 75 now--started Volvo ownership at 28 with a 1965 544 and then went through many 122 and 140 models. An SU carb in my hands is much more familiar to me than anything Volvo from about 1981 on. - Dave