Harpooning the dreaded octopus!

I’m toying with the idea of getting rid of that abomination of a fuel delivery system on my XJ1100. I cannot do any adjusting on the #2 carb without pulling my tank and setting up my test rig. I was thinking I should be able to simply sub in some XS1100 petcocks and be done with it. Has anyone here done this before? Any “gotch-ya’s” I should know about?

 

I'm not familiar with this octopus you speak of but would like to see a picture of it. If you could take a photo and post it up here it would be much appreciated.

 

The XS has a MUCH simpler setup.

The XJ1100 setup:



The XS1100 setup:

 

CORRECTION!

The XS1100H has the simpler setup. The LH and SH models have the same octopus that the XJ has.

 

yeah, i was going to correct you about that... my xs special has all the nonsense on it

 

WHAT IS all the "extry" plumbing for anyway? Is it additional fuel delivery capacity for the big mill or is it some sort of evap system? I'm just curious (550's are much simpler.)

 

As best as I can tell, Yamaha simply moved the diaphragm vacuum valves located on the XS1100H petcocks to a single unit for the LH, SH, and XJ models. The vacuum source is now from the #2 carb as opposed to the #1 and #4 carbs with the 'non-octopus' setup. Both systems appear to allow extra fuel flow for high load conditions so I don't see any reason why it cannot be modified.

 

Wow! What a mess. Not knowing anything about why Yamaha did this, I'd guess that the fuel tank doesn't have a cross over so they did this to prevent fuel starvation. But why the return lines? Does that little diaphragm thing act as a vacuum operated fuel pump (like on small engines)? Does it need to be able to push unused fuel back to the tank? Pretty bazaar.

 

Actually, if you study the XJ1100 diagram carefully, you'll find that there is simply a 'main" and a "reserve" fuel outlet from each petcock, and the single vacuum pod operates just like the vacuum diaphram mechanism on all the other XJ-series bikes (the vacuum pod even uses the same parts)......on the XJ1100, the vacuum unit part of the petcock has been moved from the back of the petcock body to a comon, external position in the vacuum pod control unit.

The octopus of lines is merely due to the fact that there is a seperate fuel outlet port ON THE PETCOCK BODY for prime vs. main fuel flow paths......

 

So if my theory of 'extra fuel' is incorrect, I can safely ditch the darn thing and go with XS1100H petcocks!

 

Michael, you are correct about the "no extra fuel" issue....but you had better make sure that the XS and XJ petcocks are the same mounting flange size (I don't know whether they are or aren't; I would suspect that they are the same size, but just don't know)).

 

Happen to be rebuilding an 81 XS1100 H with my Dad, I will be test fitting before moving forward.

 

I tried adapting a XJ750 vacuum petcock on a XJ1100 tank... The mounting bracket of the petcock does not clear the seam of the gas tank, although the bolt pattern is the same.

the octopus is a big pain in the arse. it's hard to prime and looks like junk.

if the petcocks are not leaking, you can just trash the octopus, connect (read: disable) the PRI fittings on both petcocks with a single piece of fuel line, and run a pair of lines straight to the carbs (you can still use inline filters). You'll have to turn the fuel off after every ride... :roll: