Why does this CBR600 open the first two carbs before the second two? I had assumed that a correctly sync'd carb setup would open all four carbs at the same time, but I can see the first two open before the second two when I 'bleep' the throttle. Looking at the throttle setup, it is pretty obvious why as there is a very obvious cam setting that causes this behavior. You can clearly see space between the throttle cam connected to the first two carbs and the second two. Is this intentional or did someone mess with this bike and screw this up?

 

Someone before you made a misstep.
All 4 carbs should react as 1.

 

Looking at that picture, there should be a spring in between those two plates, where that gap is.

 

Ok. And that spring would then engage the second two carbs with a little flexibility. So that probably makes sense why this bike struggles until you really open it up.

 

Correct. And it is impossible to sync the carbs without the spring.

 

So this looks better I would think. Found a spring that works in my miscellaneous parts bin from past tear-downs. Really appreciate your help this would have difficult to figure out without your insight and expertise.

 

You are very welcome. Glad to help.

 

That is a good sign that the sync is way out. Were the carbs out? Can you do a bench sync to get them closer?

I bet it's real jumpy around town and surging.

 

Those springs get left out when inexperienced people rebuild their carbs. Have seen it before and very hard to diagnose without experience. Good job Hamlin!

You should be able to sync your carbs now...but I’ll bet it’s already quite a bit better with the spring in there.

 

Thanks Dennisgb.

It is important to note the same setup should be between carbs 1&2 as well as 3&4.

If the PO left out the one in your picture there's a fair chance they omitted those also.