Vacuum advance and "octopus" diaphragm

[Bomorr]

I've been trying to put back together a bike for a friend and we are almost there after rebuilding the motor and getting broken parts replaced.

For the life of me I can't figure out where the "octopus" is and how the petcocks and fuel lines connect to it as well as where the vaccum assist spark advance line attaches to. I have looked all around in both service manuals and diagrams online but can't seem to make heads or tails of this part.

First off can I eliminate the octopus since I don't even have it anymore and if so where do all the vaccum lines connect since it seems everything flows into the Octopus.

79 XS1100F is what I'm working on.

Thanks in advance

Ben

[DiverRay]

The advance should connect to the #2 carb BODY. It should be the only carb with a connection for a hose on the upper left side, as you sit on the bike. Carb #2 is the second from the left, as you sit on the bike.
Don't worry about the octopus, it's a PITA that you don't need. Connect the left side rear tap to the right side carb fittings, the lower fittings are for gas, and the upper fittings are a vent for the carbs, and MUST be to air or the fitting on the stock airbox. The front fittings on the petcocks should be blocked off, so they will not leak gas if you turn the petcock to prime by mistake.

[Schming]

If you're sure the bike is an XS1100F it doesn't use the Octi but the SF does.
Here's a link to diagrams: https://www.partzilla.com/catalog/ya...e/1979/xs1100f
If you do have an SF here is the Octi setup:

[Bomorr]

The advance should connect to the #2 carb BODY. It should be the only carb with a connection for a hose on the upper left side, as you sit on the bike. Carb #2 is the second from the left, as you sit on the bike.
Don't worry about the octopus, it's a PITA that you don't need. Connect the left side rear tap to the right side carb fittings, the lower fittings are for gas, and the upper fittings are a vent for the carbs, and MUST be to air or the fitting on the stock airbox. The front fittings on the petcocks should be blocked off, so they will not leak gas if you turn the petcock to prime by mistake.

This is great since I don't even have the octopus anymore.
I understand everything except the rear tap to right side carb comment what are you referring to?
Since none of the vaccum / fuel lines were there I am replumbing all of them.
If I can just cut out the octopus completely my assumption is I should be able to run direct from the petcock to the 1-2 fitting for one side and 3-4 on the other and just plug the vacuum port on the petcock and be done right?

[DiverRay]

The diagram in thread #3 is for the SF with an octopus. If you have the F model, the petcocks are different. They will have a single port for the fuel, on the bottom of the petcock, pointing to the center of the bike. There will also be a smaller port in back of the petcock, pointing to the front of the bike.
Again, connect the fuel port to the bottom "T" fitting between carbs 1&2, and 3&4. We usually cross so the left petcock goes to 3&4, and the right to 1&2 . Makes it easier to run the fuel lines. The vacuum port is the smaller one, and it will connect to the port on the intake manifold. Left side to #2, right side to #3. #1&4 manifold ports should be capped unless syncing the carbs. The "upper" "T" between carbs 1/2 and 3/4 is still the vent, and MUST be open to air. They will usually go into two small plastic fitting on the top front of the airbox.

[Bomorr]

Ok great, this makes so much more sense. Thanks for the info!

[bepenney]

The diagram in thread #3 is for the SF with an octopus. If you have the F model, the petcocks are different.They will have a single port for the fuel, on the bottom of the petcock, pointing to the center of the bike. There will also be a smaller port in back of the petcock, pointing to the front of the bike.
Again, connect the fuel port to the bottom "T" fitting between carbs 1&2, and 3&4. We usually cross so the left petcock goes to 3&4, and the right to 1&2 . Makes it easier to run the fuel lines. The vacuum port is the smaller one, and it will connect to the port on the intake manifold. Left side to #2, right side to #3. #1&4 manifold ports should be capped unless syncing the carbs. The "upper" "T" between carbs 1/2 and 3/4 is still the vent, and MUST be open to air. They will usually go into two small plastic fitting on the top front of the airbox.

I have the 79 Special..can I eliminate the octopus and retain stock air box? I understand blocking vacuum on carb #2 and blocking forward petcock ports.

[Radioguylogs]

I have the 79 Special..can I eliminate the octopus and retain stock air box? I understand blocking vacuum on carb #2 and blocking forward petcock ports.

Yes.

You already know everything you need to know to delete the Octy.

The airbox will not be affected in any way.

[DEEBS11]

I have used this type for about 10,000 miles and they work great. Manual shut off.

[DEEBS11]

https://www.ebay.com/itm/223812507787

[Radioguylogs]

I use the one Deebs posted on a few of my bikes and I really like them.

However, there is no left and right versions, so some folks might not like the the way one closes to the front and the other close toward the rear.

[jetmechmarty]

I believe the bolt spacing on the early XS650 is the same as the Special. Left and right are available for those. The manual taps for a standard are not.

[Mathh]

I also know of someone on Ebay Germany ("der Muede") selling left and right versions. but I have no clue if they are for the 650 but he is too expensive.. 61 euros each last time I checked...