Question about fuel lines

[RichV]

I'm dealing with a modification done by a previous owner to the fuel system of my 81 XS1100 Special. It seems that the fuel lines run for the petcocks directly to the junction between the carbs. The left does to the left two carbs and the right to the right two.

Other than the obvious problems this would cause when the tank is low, is this a reasonable mod? Right now it's working (as near as I can tell).

When I look at the stock fuel line configuration I get a headache. It looks way over complicated for the task. Is this really needed? Is there a mod that everyone performs?

As some of you know, I have two XS1100's that I'm trying to make into a single operational bike. So far, it's working. I have the original lines from the one bike but some of the connectors are broken (age). I can make it original if needed. Any suggestions?

[DGXSER]

Look at post #5 in THIS thread for the stock fuel line diagram for your SH.

I have never liked the Octy and all of its assorted fuel lines, being a fan of the KISS method. So, I always add in line fuel filters similar to THESE.

I also run one fuel line from the left petcock rear outlet to the fuel T between carbs 1 and 2. Similarly, I run one from the right rear petcock outlet to carbs 3 and 4 fuel T. I have no problem getting that in line fuel filter between the air box boots.

All sounds pretty similar if not the same to what you have.

[fredintoon]

I'm dealing with a modification done by a previous owner to the fuel system of my 81 XS1100 Special. It seems that the fuel lines run for the petcocks directly to the junction between the carbs. The left does to the left two carbs and the right to the right two.

Other than the obvious problems this would cause when the tank is low, is this a reasonable mod? Right now it's working (as near as I can tell).

When I look at the stock fuel line configuration I get a headache. It looks way over complicated for the task. Is this really needed? Is there a mod that everyone performs?

As some of you know, I have two XS1100's that I'm trying to make into a single operational bike. So far, it's working. I have the original lines from the one bike but some of the connectors are broken (age). I can make it original if needed. Any suggestions?

Hi Rich,
there's two groups of XS11 Special owners:-
The obsessive-compulsive purists who keep their Octopus Valve system in all of it's original 9-tube glory
and the KISS guys who throw the entire thing away and install something sensible.
Simplest fix:- Cap off the carb. manifold vacuum feed and each petcock's prime feed tap.
Run a gas line from each petcock to the appropriate carb feed Tee.
Just like 15 year old low mileage tires, even if they still seem usable ALL your existing gas lines are past their best before date.
Replace the lot with Tygon fuel line.
And remember that the fuel will need to be switched manually.
Remembering ON is easy, as it'll start to falter in a hundred yards or so if you don't.
Remembering OFF needs the same mental discipline that we all used to have some decades ago when all gas taps were manual.

[BA80]

Other than the obvious problems this would cause when the tank is low, is this a reasonable mod? Right now it's working (as near as I can tell).

I ran the octy for years and this summer I just got tired of having to replace the diaphragm every year or so and scrapped it. It was in the way when adjusting the carbs anyway.

Running one petcock to 1 &2 and the other to 3 & 4 worked good until I got down near reserve then one side or the other would run dry before the other and I would end limping into a gas station on 2 cylinders. Took care of that by putting a T in each line and running an equalizer between the 2. It works great.

[TopCatGr58]

Hey Rich,

I'll only add that to allow room to actually get to the fuel lines when lifting up the tank before disconnecting, I run the right petcock to the left pair of carbs, and vice versa...running the lines across and around the intake manifolds complete with inline filters. Like Greg said, it may be the ethanol that's destroying the vac. valve in these things prematurely!

I have both spouts connected with a "Y" fitting vs. capping one off, YMMV, the rear will provide flow in Reserve, the front one is only PRIME, but it's not needed when you don't have the Octopus.

T.C.

[BA80]

Hey Rich,

I'll only add that to allow room to actually get to the fuel lines when lifting up the tank before disconnecting, I run the right petcock to the left pair of carbs, and vice versa...running the lines across and around the intake manifolds complete with inline filters. Like Greg said, it may be the ethanol that's destroying the vac. valve in these things prematurely!

I have both spouts connected with a "Y" fitting vs. capping one off, YMMV, the rear will provide flow in Reserve, the front one is only PRIME, but it's not needed when you don't have the Octopus.

T.C.

You misunderstand what I was saying about the T's. The front nipple is still capped off and unused. I'm speaking of making the two fuel lines into an H pattern. The crossbar on the H being the equalizer between the 2 lines thus equalizing the fuel in the 2 sides of the tank when it's low enough to switch to reserve. Understand?

The octy does this by design.

[TopCatGr58]

Hey Greg,

No....I did understand your description completely, was just providing an alternative albeit simpler routing design. He lives in a metropolitan area, plenty of fuel stations all around, so hopefully he won't have to worry about having to go into RESERVE too often. Also, I think the Standards have a more prominent separation of the two halves of the tank and so it's easier to get different amounts of fuel trapped in the reserve pockets. He has a special, they still have a separation, but I don't think it's as deep.

Your design is good in equalizing the fuel supply from either side before it gets to the carbs when on reserve. Just so he/Rich can understand and visualize your idea....the 2 rear spouts are run together into a "Y/T" style fitting, and then a second T/Y fitting is is connected in reverse to the single line off the first "T/Y", so that the second connector can then supply both carb nipples. "WE" know that a single petcock and 1/4" line can supply more fuel than all 4 carbs can use at WOT, so there's no worry about a bottleneck affect at the 2 -1 to 1-2 connections/lines before they get to the carbs.

T.C.

[BA80]

HA HA HA..........Analyze it all you want, it solved my problem.

I was having occasional fuel delivery problems on the highway particularly when the tank was getting low. Equalizing the lines solved it. Hasn't hiccuped since

[RichV]

Thanks for all the good advice. I have every intention of replacing the lines.

I tend to agree with using an equalizer. It's a common solution on a lot of bikes.

So just so I have this straight I could run the lines from the two petcocks rear supplied to a "T" junction. Then connect a single line from the "T" to another "T" which then run the two lines to the carbs. I guess this would be an "I" configuration rather than the "H".

Does this sound right? Will the reserve still work on this rear line?

As for the inline filter, do you use two (one on each supply after the petcock) or can you use just one between the "T"s in the "I" configuration.

[BA80]

Yes, the rear tap works on, off, and reserve.

[RichV]

Do I really need to install inline filters if the filter's in the tank look okay?

[GLoweVA]

The filters on the towers aren't as restrictive (filter abilty wise) as inline filters and may allow more fine particles thru.

Since you're just starting this build i would highly recommend some filtration to minimize the future carb 're-cleaning' that may occur without filtration.

To add onto Greg's discussion, i'm thinking of putting in some t's also to balance out my flow. One side does drain down faster than the other or at least that side doesn't like the lower fuel level, so i have to switch it to reserve well before the light come on.

I suppose you could turn one reserve on, then when it runs dry switch the other on. You'd have a double reserve. Though it probably wouldn't extend the range at all.

[fredintoon]

Do I really need to install inline filters if the filter's in the tank look okay?

Hi Rich,
need to? No. Would it be a prudent thing to do? You betcha!
in-line filters usually have finer filtration than the in-tank filters.
And in the rare but not unknown occasion that the in-tank filters fall out of the gas taps to lay on the bottom of the tank
the in-line filters will be the only ones you have (and yes, that DID happen to me.)

[BA80]

Look around, they make some really small porous stone type filters for lawn mowers no bigger than your thumb. That's what I use.

It's much easier to install a couple $3 filters than it is to tear down carbs because of a tiny particle of crap in a float valve.

To add onto Greg's discussion, i'm thinking of putting in some t's also to balance out my flow. One side does drain down faster than the other or at least that side doesn't like the lower fuel level, so i have to switch it to reserve well before the light come on.

That's part of the issue I was having George. The equalizer solved that and I don't have to switch to reserve until after the light comes on now. I pushed it to 130 miles on reserve on the way to XS Southeast once without issue.

[DGXSER]

I learned the hard way myself to always use the in line filters. As has been stated, the bike will run without them, may run fine for a while, may run fine for years without them. Or you may find yourself cleaning carbs twice a year or more if your tank has some crap in it, or you get some dirty fuel. I have also seen the top of the filters in the tanks come off, so you get unfiltered gas until the level is below the filter tops.

I formation, H formation ( run the fuel line from the tank to one side of the straight section of the T, the other ide of the straight section to the carbs, run a piece of lien between the two branch sides of the T's), any way you want to pipe it, the concept is simply to tie the two fuel supplies together. I have not done it, I just add fuel when I get about 80 miles on the tank. But there is nothing wrong or harmful about piping the fuel system that way.