Help, Gas coming out of Airbox?

[3Phase]

Dozerr,

Congratulations on fixing the carburetor leak! Those can be maddening!


Okay, the engine won't start and:

You know it doesn't have spark because you checked for spark

or

The engine cranks and doesn't start so it might not have spark?


If you haven't already checked for spark, the first thing you need to do is check for spark. Remove one spark plug wire and put a screwdriver in the spark plug boot. Put the screwdriver on the valve cover and take your hand off of the screwdriver, then crank the engine and watch the screwdriver and valve cover to see if there are any sparks sparking anywhere!

.

[Ben Geutskens]

Leaking membrane?

My XS 1100 Eleven Special (SF), Canadian version, had the central vacuum supply unit blanket off. I placed a new membrane valve and noticed gas dripping out of the air filter housing. This was NOT caused by a hanging float needle. The gas dripped out through the vacuum tube (for controling the fuel, not the ignition advancement) into cyl #1 inlet and flew back into the air box which has a drain hole with filtering foam. This happened only in the PRI position, not in the ON or RES position. In the PRI position the hydrostatic pressure from the gas works on the membrane; this is not the case in the other positions. In my opinion the only cause can be a leaking daphragm. Bought a new one. Same problem. I've read the same problem on other forums. Maybe the second membrane has also a leak.
I was Lucky to have fitted a transparent tube, so I could see the gas flowing down from the vacuum chamber to cil #1 inlet.
Has anyone any comments, same experience, cause, remedy or solution?

[Ken Talbot]

Ben - have you double-checked the plumbing of all the various fuel and vacuum hoses?



Prime setting on the petcocks should never send fuel anywhere near the diaphragm, nor even the octopus. On position will send fuel to the non-vacuum side of the diaphragm and would cause a leak down the vacuum line if the diaphragm was torn.

[Ben Geutskens]

Membrane

I'll check again. Thanx

[Ben Geutskens]

Membrane

I have no experience with this bike, but after having looked to Octopus' connections, my believe is:
In the ON position gas flows from the long pipes in the tank through the rear petcocks to the valve which opens when the engine creates a vacuum.
In the RES position gas flows from the short pipes in the tank through the front petcocks to the valve which opens when the engine creates a vacuum.
In the PRI position gas flows from the short pipes in the tank through the front petcocks to the carburetors, but through the T-connection the gas pressure is on the non-vacuum side of the membrane. See diagrams.
As (besides the vacuum line) all arms of the Octopus end up at the same side of the membrane, I cannot see how gas can flow through the vacuum line if the diaphragm is not leaking. I'm not sure the diagrams will show up.
[IMG]C:\\data\scans\Yamaha-ON-bew.jpg[/IMG]
[IMG]C:\\data\scans\Yamaha-RES-bew.jpg[/IMG]
[IMG]C:\\data\scans\Yamaha-PRI-bew.jpg[/IMG]
Am I missing something?

[DGXSER]

Vacuum valve (OCTY) operation, the fuel flows into the two center lines of the OCtY into one hole. The vacuum diaphragm is attached to a cylindrical plunger with an o ring on it that is pushed by the spring on the vacuum side of the diaphragm into the hole, blocking the flow of fuel when no vacuum is present.

Then vacuum is present, the diaphragm is pulled back, along with the plunger, allowing fuel to flow in, and reach the outlet tubes on the either outer side of the OCTY.

Petcock operation, Both ON and RESERVE flow to the rear outlet of the petcock ON feeds from the higher filter side. RESERVE flows from the lower filter side. PRIME feeds to the front outlet of the petcock and gets fed from the lower filter.

The rear outlet of both petcocks feed to the center inlets of the OCTY. The outer outlets of the OCTY feed into one side of a T. The front or PRIME outlet of the petcocks feed to another side of that T bypassing the OCTY. The outlet from the T goes to the carbs. This allows the carbs to be fed from either the PRIME outlet, or the OCTY outlet.

[Ben Geutskens]

Membrane

Sorry, there was a typo with the RES pos. Should have been rear petcock.
So, at least my understanding of the system is correct.
Do you agree that the only way gas can be leaking out of the vac line is through the membrane? That was the bottom line question.

[Ken Talbot]

Yes, the only way fuel should flow from the vacuum nipple is if there is a problem with the diaphragm membrane. This is even more puzzling when you consider there are two membranes, not just one, and they would both have to be compromised.

Have a look at this image:



You'll see that there is a white plastic block between the two aluminum halves of the octopus assembly. There is a rubber membrane on each side of this plastic block. The membrane to the left (vacuum side) pulls the valve body open when vacuum is applied. The membrane to the left (fuel side) keeps the fuel in a chamber on that side of the assembly. Fuel comes in through nipples #1 and #2 from the on or pri nipples on the petcocks. With no vacuum applied, fuel won't get past the rubber o-ring on the end of the diaphragm valve assembly. When vacuum is applied, the valve body moves to the left, which unseals the o-ring, and allows fuel to flow back out of the octopus via nipples #3 and #4.

When you talk about a previous owner blanking off the assembly, I now wonder if he may have actualy removed the plastic block?

Is there any chance you could post a few photos of your octopus? It would help to see one like mine above, and at least one more showing the assembly taken apart and the parts laid out in sequence from left to right.

[Ben Geutskens]

Thanks Ken.
The picture shows a plastic greenish stiff thick sheet with a dome-formed shape. This was used together with the kork gasket to blank off the vacuum section.
At the right hand side you see the double membrane I bought. I fitted it in between the Octy housing and cover. I guess the 'block' you speak about must be ring shaped, to get a membrane at each side. I have no problems running the engine on either ON or RES and I can block the system off again, of course, but it is just interesting to understand.

[DGXSER]

Hi Ben,

HERE is a link to a thread I put together on rebuilding the Special petcocks and the OCTY. IT shows pics of the components.

[Ben Geutskens]

You have been a real help to me. Thanks!
I bought the membrane from Georgefix as well.
The strange thing is that the plastic part was fitted, but without the hole!
I'll make a hole in it on my lathe (estimate the diameter) in it and refit the membrane.
It looks like the membrane has been overstressed, due to the absence of the plastic part. As I cannot see a leak, maybe the membrane material was pulled apart around the valve stem. I'll aplogise to Georgefix who sent me a replacement.

[Ken Talbot]

If you look again at these two pictures of the plastic block:





You'll see a small hole in what is the bottom part of the block. This is an atmospheric vent for the chamber between the two membrances that allows the valve assembly to move. When vacuum is applied to the vacuum membrane, is pulled over against the spring and a wee bit of air enters the chamber between the two membranes. When the vacuum stops, the spring pushes the valve body and o-ring back over to stop the flow of fuel and the bit of air that was drawn into the chamber is expelled.

[Ben Geutskens]

Sounds logical, thanx.
I had to make the spring myself by the way, çause it was missing.
I'll report later when I made the changes.

[Ben Geutskens]

The plastic plate which I have will not work, as the notches that stick into the small membrane holes are missing.
I'm looking for the plastic membrane support, but want to be sure if the one used on the vacuum valves is the same as the one in the "Octopus".
Anyone knows this?
Anyone knows one for sale?
http://www.mijnalbum.nl/index.php?m=fto&a=73&id=373079491&key=YJG7HUOE.jpg

[Ben Geutskens]

The plastic plate which I have will not work, as the notches that stick into the small membrane holes are missing.
I'm looking for the plastic membrane support, but want to be sure if the one used on the vacuum valves is the same as the one in the "Octopus".
Anyone knows this?
Anyone knows one for sale? See pictures.
http://www.mijnalbum.nl/index.php?m=...y=YJG7HUOE.jpg
http://www.mijnalbum.nl/index.php?m=...y=LAFQJTTC.jpg