Carb Issue

[rwingsfan]

Was looking at a friends XS, it is a 78 with stock bs 38's. It has a very high idle (around 2000-2500 rpm) idle screw all te way off. I rest the air mix screw, tried 1 1/2 to 3 turns out, amde no real difference. I then pulled the filters and found that the left side when covered will suck right in and die, but the right side can be covered and hardly no suction at all, does'nt even hardly affect the way it runs. I am having a run on carb issues as my personal ride is looking for a good set also. Ideas where to start?

 

[bdholsin]

I'd start at looking at valve clearances. It's easy and could possibly explain the lack of suction on the right side. Intake valve could possibly be out of spec and not sealing to the seat.

 

[5twins]

Check the carb sync. Sounds like the right carb is running faster than the left.

 

[5twins]

Actually, after giving this some more thought, I think it's just the opposite. The left carb's butterfly plate is open more and it's running faster than the right. As you back out the idle speed screw on the left carb, it closes both butterflies together or in unison, reducing your idle speed. If one butterfly is open less than the other, it will close completely and stop the idle speed screw from having any more effect on idle speed. So, your right butterfly is closed and basically shutting that carb off. That's why you feel little or no "pull" from it when you put your hand over it. Your left butterfly is still open enough for the bike to rev at 2+K.

 

[Sundie]

5T: Just say "balance them" - that should cover all bases.

 

[rwingsfan]

For sure a sync issue. His intakes have no barb so I can't hook up the manometer, but I adjusted the sync screw anyway and got it much better. I think you were right on. I can now get a good idle and everything settled down. Ya Sundie...balance them for sure

Check the carb sync. Sounds like the right carb is running faster than the left.

 

[5twins]

I thought I did say that, lol.

 

[XSLeo]

I think on they have a port for syncing. It is plugged with a straight slotted screw. Just above the throttle shaft.
Leo