80 xs11 special carbs sync

[probstct]

Yes it does. It's plumbed to the intake.

This what the plumbing is supposed to look like:

This is how I have it plumbed.
I just don't understand the flow/ vac.

[jetmechmarty]

Hose #2 is vacuum. One end goes to the back side of the fuel shutoff valve. The other end goes to the #2 intake. When the engine starts, the intake is sucking on that vacuum hose. The vacuum pulls on the diaphragm in the shutoff valve allowing fuel to flow to the carburetors.

[DGXSER]

One minor correction, you are correct that when you hook up the vacuum for carb synching, you will not have vacuum to the Octy or Vacuum operated fuel valve shown in the diagrams, as line no 2 is disconnected from the intake boot to attach your synch gage.

As Bug suggested, this is where the PRIME setting on your petcock is used, it bypasses the OCTY and lets fuel flow straight to the carbs.

Looking at the diagram, when your petcocks are in the ON or the REServe settings, fuel flows from the rear nipple on your petcocks. That nipple lets fuel flow to either the number 2 or 3 inlets of the vacuum valve (OCTY) via the fuel lines labeled 4 and 5.

When the engine is not running, there is no vacuum pulling on hose 2, and therefore the diaphram valve is not pulled open. There is an o-ring on a "nipple" of the diaphram that plugs ports 2 and 3 of the valve stopping the fuel from flowing into the valve when no vacuum is present.

When the engine is running, the vacuum in hose 2 pulls the diaphram toward the engine, pulling that o-ring open to let fuel flow from ports 2 and 3, this lets fuel flow out ports 1 and 4 to lines 7 and 8, into the Ts shown and to the carbs through the two lines labeled 3.

When your petcocks are in the PRIME position, they allow fuel to flow out the forward nipples on the petcocks, into the fuel lines labeled 6 on each side, then into the Ts and to the carbs through the two lines labeled 3. Bypassing the vacuum fuel valve, giving you fuel flow to the carbs without the engine running.

Of course, when the petcocks are set to the OFF position, no fuel flows to either petcock nipple.

The purpose of the vacuum valve is to allow you to leave the petcocks in the ON position and still not have fuel flow to the carbs when the engine is not running.

Look at THIS thread, about half way through is where I tore down the OCTY and you can see the diaphram and the internals of the valve.

[probstct]

One last question, does anyone have the part numbers for the rebuild kits?
octy & petcock
Again, thanks for all the advice and instruction, hopefully I get her back on the road SOON.

[natemoen]

This will do both petcocks and the octy.

http://item.mobileweb.ebay.com/viewi...d=360463280607