Air inlets on carb boots, should both be connected too petcock?

walleye

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Hello all,
Just a quick brain pick. Do both air inlets on the carb mount boots both need to be connected to the petcock or should one be capped off?
I have an sohc 1980 se us custom which I'm still trying to get running.
At the moment it still has both inlets connected but after perusing the manual diagrams indicate that one inlet is capped?
Unfortunately I dont know the exact origin of the engine so could it be dohc?
All help appreciated!
 
Hello all,
Just a quick brain pick. Do both air inlets on the carb mount boots both need to be connected to the petcock or should one be capped off?
I have an sohc 1980 se us custom which I'm still trying to get running.
At the moment it still has both inlets connected but after perusing the manual diagrams indicate that one inlet is capped?
Unfortunately I dont know the exact origin of the engine so could it be dohc?
All help appreciated!

won't be dohc, it won't fit.

one is capped and the right side is the vacuum barb/pipe which runs under the tank
 
When you are sitting on the bike....facing forward (to be clear), the petcock is on the left side, as is the choke knob. The left carb boot barb goes to the petcock, the right is capped.
 
I hate to jump in here but does the tube that connects to the petcock have to be connected? Or can I just plug it?

If you want your vacuum petcock to work right, it has to be connected. If you replace the petcock with a manual one (I did) both barbs can be capped, actually, they need to be capped in that situation.
 
Actually it doesn't matter which on is connected and which capped, it just needs to create vacum..
 
If you want your vacuum petcock to work right, it has to be connected. If you replace the petcock with a manual one (I did) both barbs can be capped, actually, they need to be capped in that situation.

Thanks for the help.
Both inlets are currently connected and this probably explains why I'm not getting enough fuel through to fire up!
Incidentally where did you get the manual petcock from? Any links you could provide?
I'd like to replace mine, it would simplify things and thats always good!
 
I'm not sure as it really matters all that much which side barb you connect the vacuum line too just as long as it is on one and the other is plugged. As drewpy said though there are metal holders on the underside of the tank to cross the line over.
 
I'm not sure as it really matters all that much which side barb you connect the vacuum line too just as long as it is on one and the other is plugged. As drewpy said though there are metal holders on the underside of the tank to cross the line over.

Yep, that's right- doesn't matter as long as the line reaches.
 
My 79 is on the left and the 80 is on the right:laugh: Just to keep it equal.
 
Sorry to revive an old thread, but I'm wondering if I have to cap the extra barb. Can I instead use a manual petcock and run a vacuum line between the two barbs?
 
If you run a manual petcock, cap both of them. You won't be able to sync the carbs well if they are both connected.
 
As a counter point to what Hough correctly stated, after you have the carbs sync'd, try connecting the barbs with a vacuum line and see how it responds. There are many bikes that idle and decelerate smoother with a "balance tube" between the carbs. What will it hurt to try it out?
 
I know some of the xs650 guys do this but the 650 has a 360 crank and the 400 has a 180 crank.:shrug:
 
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