Lol, no the C20LET is a Vauxhall engine (from a Calibra/Cavalier turbo)
The engine is a Subaru EF12! It has a Hitachi carb, which is two barrel. The primary opens on a lever from the pedal, but the second opens using a vacuum from a dashpot - I've tested the dashpot by blowing into it and the lever moves.
The car moves well, even on full open throttle - I believe it is running much better now than when I got it, but it just isn't idling correctly (which is now making me think there IS an airleak like su7ajones says), or something isn't working. I bought some easy start and will try it out tomorrow.
The carb has a duty solenoid which opens a valve in the carb which controls the fuelling/slow air bleed inside. These are known to be dodgy I think.
After running the engine for 20 minutes while I messed around, I revved the engine to 8,000rpm (it's a 3 pot 1.2), and it got there as normal ...
I can tolerate the naff starting (requiring depressing the pedal slightly), and the slight hesistation (esp around corners - fuel starvation?), but the rpm makes it silly to run.
Thanks for your help!