bing carbs

Iam confused according to what I read in manuals the throttle spring holds the carb in the full open position however on mine the butterfly valve is in the closed position this cant be wide open or can it? These are bing CD carbs on a used 912 engine I do not what it was in before or how it was set up.Thanks

The factory configuration has a spring which pulls the throttle wide open. The theory behind this is if the cable breaks, it is better to have full power than have the engine go to idle.

The throttle cable holds the position of the throttle against the spring - that is why you see a lot of vernier throttles on 912s rather than twist/friction locks which have some potential for slipping.

Is this a used engine? if so, you might find that the setup has been modified or is missing something.

Attached is a new-out-of-the-box 912ULS - should be able to see the throttle arm forward (open) pulled into that position by the spring forward and below the throttle arm.

Your not looking at the choke butterfly are you, I have no idea if they even have one.