My dual dellortos have springs on them, and they snap back fine when throttling by hand on the linkage crossbar. But, when throttled by foot, it doesn't seem to snap back and throttle down. So is a spring typically required to overcome cable friction, or does this just mean my cable is crap?

with a terry cable, and weber carbs, i did not ever require a return spring.

for a wicked snappy cable, check out the crossbar springs at airkewld.

My dual carbed setup required an extra spring on center of the crossbar, hooked to the back wall of the engine compartment. Might give you a real stiff pedal though.

I am running dual delortos with a terry cable and no extra springs. I had an OEM throttle cable (brand new) when I put the carbs on and the friction was very bad. The terry cable fixed that.