Fuel line / air line connections

[uk1.1s]

Dumb Question from me today!

I have a late XS with the octopus fuel line arrangement. Been having some real hassle in getting it running properly and took off the octopus around six months ago which seemed to improve things.

Have recently installed new float valves, which I've found need some adjustment as fuel is still getting through the carbs and ending up in the sump with the oil.

I'm going to take my carbs off (again!) this weekend and get the float height right across the lot corrected and am thinking of putting the Octopus thing back into service.

So - my question(s).

I've seen some contradicting information on how the fuel lines connect up between the octopus and taps. Has anyone got the definitive guide?

Is it a simple job of setting the tap to prime - looking where the fuel comes from and connecting the carb supply line up to this and vacuum side on the other connection to the fuel tap?

I'm a little sceptical about putting back the octopus - does anyone have advice on if it's a good idea or not.

Cheers - Graham

[Ken Talbot]

Here's how Yamaha draws it:

[uk1.1s]

Yamaha diag

Thanks Ken

That's the drawing I'm currently going by - however, I have seen alternative drawings in the passed (no so detailed) that swap the fuel lines over at each tap....... hmmm

If there is a difference between models then I wondered if there was a simple test I could do to be fully sure. That's why I mentioned the 'Prime' position test.... does it make sense to switch the tap to prime - see where fuel comes from and assume that is the fuel supply side. Personally I can't see why not.... but you never know I could be missing something !

[Racer X]

That drawing is correct.

I just put mine back together after being apart for two years. I deleted and capped off the prime circuit. I thought he only time you need it is on intial float bowl fill-up. I was hoping that the reserve does not use it. It makes the hose nest under the tank seem a little smaller.

[Duster]

Spider

Gram; I bought my 79xs11sf with out the spider on it and found that if a float filled with fuel or trash entered the float needle, if the fuel is left on it could fill the cylender, airbox and empty the tank. I put the spider on according to the diagram Ken sent but still had fuel free flowing to the carbs. My fuel cut off were swithched so I had to switch the fuel line front to back and now it's working great. The thought I missed is fuel has to go through the spider before it goes to the carbs or it would be like leaving it on prime. Duster

[Mike Hart]

Graham, I think all versions of the octopus were identical. IIRC, prime and reserve come out of the same tap, the front tap is ON, the rear tap is Prime / Res.

Here's what I did:


That's a 90-degree shut-off. No more gas in the sump, ever (as long as I remember to turn off the one red tap!)

[Racer X]

You get enough fuel through just the one 1/4" hose to feed all four of those carbs under all conditions?

[uk1.1s]

Thanks Guys

Thanks for the info guys - will have a look at it next time I've got a spare hour or two

[Mike Hart]

Originally posted by Racer X
You get enough fuel through just the one 1/4" hose to feed all four of those carbs under all conditions?

Yes. I flow-tested before I hooked it up. Gravity flow thru 1/4" hose/fittings was 20 oz/min, that's 5 gallons in 32 minutes.

So, it depends on your gas mileage and how long you can hold the throttle wide open. If you can keep the throttle wide open long enough and get only 10 mpg, you might need a bigger pipe.

I've seen absolutely no starvation symptoms at full throttle.

BTW, many new-ish bikes have only one ~1/4" hose feeding the carb bank, like f'rinstance my 1200cc Bandit that has larger carbs and larger main jets.

[jkgrubbs]

Mike,

Sexy Solution!

Where do you bolt on the bracket for the 90 degree valve?
My assumption is that you leave the petcocks on the tank on, and run the two lines on the angle tees to them, relying on the tank screens, no external filters. Is there room for a small screen filter, like a disc screen from a Briggs and Stratton mower engine?

[Mike Hart]

Originally posted by jkgrubbs
Where do you bolt on the bracket for the 90 degree valve?
My assumption is that you leave the petcocks on the tank on, and run the two lines on the angle tees to them, relying on the tank screens, no external filters. Is there room for a small screen filter, like a disc screen from a Briggs and Stratton mower engine?

Here's how it looks installed:


The airbox on the XJ had a mounting point behind the side cover that was perfect for the bracket.

A large single filter could go between the single line and the tee that splits to the carbs. Or two smaller ones elsewhere.

[jkgrubbs]

I wondered if there was room, I see you run indy filters. I still have the stock box, I like the gold, but it gives me ideas...and that's a dangerous thing!

[TopCatGr58]

Just be careful with the Indy Filters you get. DEO's XJ that I helped get the gears right had a set of cone filters, but the rubber lip was flanged in too close to the intake vents and ports, and decreased performance, wouldn't go over 7k. Did nothing else but take them off and took a test ride, and it ran to 8.5 K + with no problem or hesitation. Can't remember what brand his were, believe they were generic, vs. K & N!? YMMV.
T.C.

[Mike Hart]

emgo 54mm are inexpensive and work. Went thru this with Ken (ratbyk) and others. Some do indeed interfere. EMGO do not. Bill Kingson has/had them, I do on my XJ, others do, no prob.

K&N makes pods of various kinds, but are they worth the money? You decide. (I run the K&N dual pods - 2 carbs each pod - on my Bandit, they flow and filter great)

K&N filter in stock box w/ holes drilled in airbox is probably just as good, quieter, and there's something to be said for the stock look.

I like the indi look and the carb noise myself...

[jkgrubbs]

Thats just it. I do like to see the gold, that's one of the things that drew me to the Midnight. I do have a k&n right now, and the octo and petcocks seem to be hunky-dory. We all know the mantra, if it ain't broke, don't fix it. I try to do bunches of reasearch before I act, and will file this away for future reference. If the octo boogers up, this is one option to try. The expertise here has been invaluable, and will continue to be. Right now I am painting the tank, (rattle cans, Plasticote seems to do better than any other) and I was thinking, as long as I had the tank off, but I just wanna ride. It is going back together today.