octopus diaphram fuel set up

[vintagemcyclegu]

Does anyone know the reason for this wierd set up. Was there a reason for it. It just seams like more parts than are needed to send fuel to the carbs.

[bikerphil]

It automatically shuts the fuel off when the engine is off. Many of us remove it.

[DGXSER]

As Phil stated, it is a safety/convenience device. It is a vacuum operated diaphram in there that without vacuum, a spring keeps a plunger with an o-ring pushed against the hole where the 1 and 2 (gas lines form the petcocks) feed the "Octy". This keeps fuel from flowing out 3 and 4 (on the outside) and going to the carbs. Of course, this is if it is piped up and operating correctly. Thus saving the operater from having to turn those pesky petcocks on or off at each end of the ride. Also saving the owner form finding an engine or air box full of fuel whne a float valve fails to hold while parked.

But that spring gets weak and the fuel will dribble past or gets really weak and it FLOWS past. Or someone puts the lines on wrong. And then it is just a piece to leak or cause trouble.

So again as Phil stated, alot of folks ditch it and just run the back petcock outlets (being the on and reserve outlet) to the carbs directly, with an inline filter usually.

[Lamric]

Having the octopus means that the Specials only have one vacuum valve that can leak, the Standards have two, one in each fuel tap.

'nother reason for the octy is that it splits the fuel flow from either tap to all four carbs. So, when you are running out of fuel on the motorway/highway you only need to turn the left tap to 'Reserve' and it will feed all four carbs.

Same thing works when you need to 'Prime' the float bowls before starting the bike, you only need to turn one tap.

In fact you can ride with the righthand tap switched 'Off' and have no problems. So I wonder why they put two taps on the Specials.

[natemoen]

I guess personally I would prefer 0 vacuum valves...

[BigRed]

In fact you can ride with the righthand tap switched 'Off' and have no problems. So I wonder why they put two taps on the Specials.

There are two taps because you won't get all the fuel out with only one tap on. You are correct that switching just one side to prime or res will feed all four carbs, but that tap will run dry while there's still a little fuel left on the other side of the tank.

I've rebuilt my octy, but haven't reinstalled it yet. I plan to just because I've had the floats leak gas many times (they've since been rebuilt as well) and I'm concerned about burning my house down.

[XS1100_OEM4ME]

BigRed

There are two taps because you won't get all the fuel out with only one tap on. You are correct that switching just one side to prime or res will feed all four carbs, but that tap will run dry while there's still a little fuel left on the other side of the tank.

I've rebuilt my octy, but haven't reinstalled it yet. I plan to just because I've had the floats leak gas many times (they've since been rebuilt as well) and I'm concerned about burning my house down.

I am with you BigRed, if motorcycle carbs "never" leaked they would not have petcocks, just a low fuel light, like the XS1100's do have. The octy lets me get off my bike, put down the stand, take out the key go have some beer's and come back without finding a pool of gas under or inside my bike. I bought a XS in 79 and thought the octy was the best thing sence sliced bread (had forgoten to turn off petcocks on past bikes with poor results)

[jetmechmarty]

I too, have a tendency to forget to turn the fuel off. When my "octy" failed, I purchased a new one. I have had an XS650 since new. It has the vacuum petcock that is original to the bike. That valve has functioned for 27 years as I post this.

[XS1100_OEM4ME]

Octy

Does anyone know the reason for this wierd set up. Was there a reason for it. It just seams like more parts than are needed to send fuel to the carbs.

Copy from other octy post, hope it helps:

1st, if you look at the octy for fuel flow, it is simple to understand. 2 lines from the petcock "on" to the octy for on (RUN). 2 lines out of the octy valve that alow fuel to flow to all 4 carbs "only" when bike is running (thus the vacume line to the octy from one carb to open or close the valve). The other two lines "T" into the fuel flow from the octy to the carb lines as a way to by-pass the octy valve when needed (like 1st start after storage or carb rebuild) It only looks complacated, it is just a check valve that can save you from turning off and on petcocks (and save your motor if the needles leak) You can find them on ebay for $10.00 with the lines attached) best to look for someone parting out a whole bike, most don't list the octy sep. but will sell/ship for a few bucks). most comlet petcock set rebuild kits come with the dieframe for the octy, good luck anyway you chose to go