Heyo, first post. Did some searching but this is kinda hard to search for..
I've got a set of "keyhole" carbs off my '78 CB750K. They appear to be clean and in good shape. I noticed that the throttle (as in the carb linkage itself; they are on my desk) doesn't quite have that quick snap throttle return action. Upon investigation and fiddling, I realized that when the tops of the carbs are removed, it has a much stronger, quicker motion. It's as if there is a vacuum in the top section of the carbs. It's not super slow or stuck or anything, its just a tad slower/heavier. And without the carb tops it's got that crisp, fast snap back. With them on, it's like there is a slight pressure against them as they move up and down.
Is this normal operation? While searching, I saw someone mention something about plates or something being installed backwards could cause this? As in air not able to flow freely in and out of the upper carb section? No idea. I've looked in there and I don't see how that throttle valve/linkage could be installed any other way.
P.S. - Is that big throttle return spring original? I've done some googling but it's hard to find clear reference pics. I saw a picture in the shop manual that shows a different style spring hooking to the carb mounting plate itself. Not sure if this big spring provides more or less strength than an original design.
