Octopus

[jetmechmarty]

What does the "octopus" do? How does it work? Why do some of you recommend removing it?

[chevy45412001]

do a search

that subject has been covered quite a lot in theese fourms. Try a search first,also might want to try the modification parts below on the main fourm page.

[Jerry]

Bikes with the octopus have vacuum-operated ptcocks. The octopus connects to a nipple on the intake manifold and routes vacuum to both petcocks. In theory, when the engine is not running, the octopus closes, which closes off vacuum to the petcocks, shutting them off. Safety feature, so if you lay the bike down or hav an accident and the motor quits, fuel flow through the carbs is shut off.

Two disadvantages with this set up: The octopus and related hoses require maintenance as they get older, and it complicates working on the fuel system. Many people have removed the octopus rather than repair it, and get the same effect by routing the petcock vaccum lines through T or Y fittings directly to the intake manifold nipple.

There appears to be no real use for the octopus other than to prevent gas from getting directly into the engine via the vacuum nipple, but I've not heard of petcock failure resulting in gas in the vacuum line. Could happen, though, I suppose.

As I have had no problems, my XJ's octopus is still in place. If you have a problem with yours leaking, or just want to clean up the under-tank clutter, you might want to remove this device.

[jetmechmarty]

I have fuel flow from my petcocks with them in the "ON" position and the engine off. After reading previous posts, I gather that I may have bad fuel cock diaphrams. Is this correct?

[chevy45412001]

very possible

thats what problem i had with mine (xj). got two gaskets only from dealer 11.00 dollars for the pair. i didn't feel i needed the whole kit which was like $24.00 per side. works fine now.

[nashville_bill]

Marty,

Don't you have a special? The specials don't have vacuum operated petcocks that the standards do and the Octopus provides the automatic function of turning the gas on and off.

Actually, the "Octopus" turns the fuel flow on and off using a single vacuum operated valve that has four fuel lines and one vacuum line connected to it. There are two fuel connections to each of the petcocks. One of the lines from each petcock goes to the supply side of the Octopus valve and the other (Prime) goes to a "T" that connects the delivery side of the Octopus valve and the carbs (1 and 2 or 3 and 4).

It is a lot of plumbing but I have it on my bike because I don't want to have to remember to turn the gas on and off and I think it works just fine.

[jetmechmarty]

So, according to Nashville Bill, it's the "octopus" that needs my attention. Do I have that right?

[John]

Hey Marty! The fuel lines are not as complicated as the one you work on. Your making too much out of nothing. Look here for the proper hose routing.
http://www.yamaha-motor.com/service/service.asp
Click on 'Online Parts Catalog" and the rest is self explanitiry. When you get to the XS1100SG page then look on the left side of the page and find fuel cock piping. That shows how the lines are plumbed.

[D. P. Larmee]

Huh???

That's the stupidest ****ing thing I've ever heard of. Let me get this straight; so as an improvement on the specials and XJs, they went from a straightforward two fuel lines and two vacuum lines that the standards have to a maze of intertwining fuel lines. But hey, you only need one vacuum line. Who ever thought this was a good idea ought be shot. Is there something that I am not getting here? What legitimate advantage could there possibly be to the octopus setup? Was it just a cost issue; only using one vacuum diaphram assembly was cheaper for Yamaha?

[pgg]

D.P. Back in the 70's, the japanese designers were in grave danger of being fired for sitting around doing nothing and resting on their laurels. They subsequently created the brilliantly conceived octupus setup. From that momentous day on, the K.I.S.S. princible was forever put on the back-burner.

[John]

One possible purpose would be to supply fuel to all carbs, even in the event that one petcock should stop flowing for some reason. I have mine removed, and the way I have the fuel lines plumbed, I can run on just one petcock, but I have to remember to turn it on and off manually.

[TopCatGr58]

Hey there JetMarty,

Regrettably, Jerry is slightly incorrect in the Specials/Xj's octopus and petcock function descriptions! There are NO vacuum lines going to the petcocks, they are plain gravity feed valves. Both supply lines from the petcocks are going to the Octy. The octy has the vacuum diaphragm/valve that opens the supply lines to the carbs when vacuum is applied. It's supposed to shut off the supply when the enginen is off. This was to allow you to LEAVE your petcocks in the ON position, and still have the fuel shut off, so as not to overwhelm the float needle valves in the carbs!

So, yes, Marty, your petcocks will flow fuel in the ON position if you are testing the lines at the tank, bypassing the Octy! Also, when you put the petcocks in PRIME, that set of lines bypasses the OCTY's valves and goes directly to the carbs, to allow you to fill the bowls from either evaporation, or whatever!

So...the big question is ARE YOU HAVING ANY PROBLEMS with your current setup? If you're not finding puddles of gas in your air filter chamber, or on the ground after parking and leaving your petcocks set to ON, then the OCTY is most likely doing it's job, although it could be leaking, and the carbs float valves are keeping it from overflowing!?

Folks who acquired Specials, or were reworking them after a long "siesta" and found the Octy defective, decided just to get rid of it instead of investing $$ in the rebuild kits!

[jetmechmarty]

Thanx TC. That clears it up. If I leave my bike in the garage with the petcocks in the "ON" position, I smell gasoline in the morning. That tells me the octopus is leaking. I can leave it the way it is and remember to go to "OFF", fix the octy, or bypass it.

Thanx again for clearing that up

[scalded dog]

Marty, keep one thing in mind, if the "octopus" is letting gas flow, and the only thing keeping it ou of your motor, are the floats, you could start getting gas into your crankcase, though I have a standard, the floats allowed gas into the crankcase, and fried the bearings, fortunately, it was my first standard, which had already suffered neglect fro the PO, so I had intended to park it anyway. I would suggest you check for gas in the oil, cut a green limb from a hedge or other bush, dip it in the oil, when you pull it out, light the oil to see if it will burn, if it does you have gas in your oil. Later 'Dog