This ain't no SU! Some sort of after-market fuel pump has been fitted (it still ticks like an SU, though), along with a Purolator Pro-fuel regulator - I set it to 3psi, so we'll see if perhaps fuel starvation was the cause of the 'hesitation waltz.' (And the discolouration you can see in the photo is dust, not rust - a sponge-down and a good spray of fish oil should keep it nice and clean)