Balancing carbs - just a quick question

cyber104

CB750 Member
Messages
22
Reaction score
9
Points
3
Location
Davidson, NC
Hello:

Quick question on balancing the carbs on an '81 750C.

Bike runs good and my vacuum gauge set indicates that the carbs are pretty well balanced but I think I can get them a bit better.

My question: Since this bike is new to me and I've never rebuilt the carbs - should I leave the mixture screws "as is" and focus just on the balance? Or should I set all the mixture screws equal and then balance?

The mixture screws may all be the same at them moment - I haven't checked. But if you guys tell me there is no reason to check them and to just balance then I'll leave them alone.

Thanks!
 
Jet,then check your plugs,start screws approx 1-1/2 out from seated all air..if bike runs good leave alone.
 
Jet,then check your plugs,start screws approx 1-1/2 out from seated all air..if bike runs good leave alone.
I don't see any reason to "Jet" a bike that runs down the road nicely. I'm just trying to smooth out the idle.

And I don't want to mess with the mixture screws if all that is needed is to sync the carbs as close to perfect using vacuum gauges.
 
I misunderstood you...synchronized carbs means they all open at the same time,..we still use mercury gauges... we start with air idle if there's any question not synchronize which I can get closer on the bench than most people with gauges,...air idle mixture is how you smooth it out, if that is the problem
 
Last edited:
Small correction. The butterflies will all open at the same time whether synced or not. The syncing is the adjustment of the butterflies to put them at a starting point, individually, the same as carb 2.
 
Small correction. The butterflies will all open at the same time whether synced or not. The syncing is the adjustment of the butterflies to put them at a starting point, individually, the same as carb 2.
Well yes all opening at the same time from the same starting point I pretty much thought that was understood, and you surely wouldn't need gauges to find that out you can do that visually
 

Attachments

  • IMG_20201005_171422.jpg
    IMG_20201005_171422.jpg
    301.3 KB · Views: 15
We are all saying the same thing I think. The linkage screws are simply used to adjust the individual butterflies so that all carbs pass the same amount of air. They all open at the same time but from different set points. It's not like a progressive linkage carb pair like you might find on an XL600R. I've tuned (3) 2-bbl Weber DCOE's on a Jaguar E-type with individual runners so I'm familiar with the process.

My question was really about the mixture screws and whether to worry about them first before making sure each carb is drawing the same vacuum.
 
I would sync first. The amount of air going through the carbs will affect the fuel being pulled into the mix by the screw. Get the sync done so the vacuums are the same, then adjust the mixture screws.
 
Back
Top