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.
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octopus diaphram fuel set up
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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.Life is what happens while your planning everything else!
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80 XS1100 Special - Project Resurrection
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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.Brian
XS1100 LG "Mr T", SG "ICBM" & FJ1200
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I guess personally I would prefer 0 vacuum valves...Nathan
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Originally posted by Lamric View Post
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.
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.'80 SG with motor from a '82 XJ
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BigRed
Originally posted by BigRed View PostThere 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.1979 XS1100 Special (Mad Max, OEM) Current
1980 XS1100 Special
1990 V Max
1982 KZ750 LTD Twin
1986 700 FZR Yamaha Fazer (faster then expected)
1979 XS750 Special (my 1st Special)
1974 CB750-Four
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1961 Catalina 389/1970 Torino GT 351/1967GTO 12to1 comp./ Roller cam/ T-10/ 456 gear/Tri-power/1967 GTO 400, 1969 Camaro, 1968 Z28, 2001 BMW M Roadster 0 to 60 in 4.5 sec. Jaguar XK8
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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.Marty (in Mississippi)
XS1100SG
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Octy
Originally posted by vintagemcyclegu View PostDoes 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.
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 go1979 XS1100 Special (Mad Max, OEM) Current
1980 XS1100 Special
1990 V Max
1982 KZ750 LTD Twin
1986 700 FZR Yamaha Fazer (faster then expected)
1979 XS750 Special (my 1st Special)
1974 CB750-Four
Past/pres Car's
1961 Catalina 389/1970 Torino GT 351/1967GTO 12to1 comp./ Roller cam/ T-10/ 456 gear/Tri-power/1967 GTO 400, 1969 Camaro, 1968 Z28, 2001 BMW M Roadster 0 to 60 in 4.5 sec. Jaguar XK8
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