Carb sync - maybe a dump question

[Niels B]

I’ve now rebuild a couple of engines and recently synced the carbs on a couple of XS650E - with great success I will say.
I’m on a 3rd ‘78 model but don’t have the linked carbs, thus considering using a set from a ‘75 XSB, this require 2 throttle cables.
Is there any reason to sync these? Should I use carb holder with air barbs ?
Since each cylinder is on the fire and compression stroke 360° apart, what’s the point of syncing them? Thoughts?

 

[WideAWAKE]

So that both carbs/cylinders work/react the same way.

 

[Niels B]

So that both carbs/cylinders work/react the same way.

I’m aware that the throttle etc need to open kind of at the same time, however when one cylinder fires the other one is 360° from fire - right ? The 75 didn’t come with an air barb on the carb holder - how did they synch them ? Or should I forget about that and just get the air barb holders and take it from there ?

 

[5twins]

Yes, you still need to sync the carbs or one cylinder will run faster or slower than the other. Yes, carb holders with barbs would be the simplest solution. Then you can hook vacuum gauges or a manometer to them for syncing.

Syncing individual carbs with separate throttle cables is a two step affair. First you must set and match the idle speeds, then you do the "at speed" sync so both carbs/cylinders run at the same speed. The "at speed" sync is accomplished by matching the freeplay in the two throttle cables. You must do the idle speed sync first because adjusting the idle speed adds or subtracts freeplay to/from the cable, and this would throw off your "at speed" sync if you had done it already. If you need to adjust the idle speed in the future, adjust each screw equally or you'll throw the sync off.

 

[Kevin Werner]

To expand just a little... The sync'd carbs will idle better, start better and run smoother.

 

[Niels B]

Thanks for the tips, I’ll get some air barb holders , if I stumble over a linked set at the right price I can swab them out !

 

[gggGary]

78 would have been linked when sold
set cables to pull at hte same time, compare how far the idle screws are out (they should match) then use the hand on the muffler exit technque to synch early carbs and VM34's. Works well enough for me.

 

[Niels B]

78 would have been linked when sold
set cables to pull at hte same time, compare how far the idle screws are out (they should match) then use the hand on the muffler exit technque to synch early carbs and VM34's. Works well enough for me.

Did kind of that on the other two ‘75 I have as they don’t have the air barb holder so sync was so and so - they run smooth so think I got it right . Was trying to figure out if there would be any benefit of the air barb and sync the individual carbs. I may go search for a set from a later model though - like the single action as it’s born with!

 

[Kevin Werner]

Did kind of that on the other two ‘75 I have as they don’t have the air barb holder so sync was so and so - they run smooth so think I got it right . Was trying to figure out if there would be any benefit of the air barb and sync the individual carbs. I may go search for a set from a later model though - like the single action as it’s born with!

There is mention somewhere here of adding vacuum barbs to carb boots. Well worth the effort for syncing carbs.