tank vent

[old paul]

Okay guys, I suggest paying attention to the Jurgenson posts. In this one he talks about the tank vent, but I spotted it too late.
(Have you checked that the tank vent is working? It is that back rubber hose going down from the right side of the tank next to the carb. Open the gas tank and blow into it. The screw-in fitting on the underside of the tank to which the hose is connected is notorious for electrolytic disintegration.)

Here is what I think happened. Last week I filled the tank, rode only a few miles and then let the bike sit in the back yard for several hours. The problem is that I live in Dallas, and the temperature that day was over 100F. The vent was plugged, the fuel expanded, the tank bowed up and now I have a huge piece of paint that has lifted.

The good news is this probably is the source of my lean surge at speed, as the fuel drained out quite slowly, even after cleaning the long filter and bottom petcock screen.

Now to decide what to do about the paint. Am thinking about a slash of white across the front edge, but am also heading off to my favorite body shop to see about a complete matching repaint of the tank.

[Bill Jurgenson]

Glad to hear that my pointer was right.

Both of mine were clogged by the crud the electrolysis created. OTOH, the red sport was not. I personally did not have that one very long, but it was 1995 and OK. Perhaps it is only a problem with the very first ones. My blue Tour is 1994 and the MZ parts except the frame of my green one are also from the first series, taken from a new Sport never used and broken for parts.
whatever.
My vent looks like this:

Vent.JPG (68.96 KiB) Viewed 2216 times

The fitting is an overthecounter item used in pneumatic control circuits:

fitting.JPG (63.57 KiB) Viewed 2216 times

The maker is Festo but any brand will do, It has a tapered thread that snugs up air-tight. The hose is also from the same source.
The blue bike is the same, altho it has the stock tank cap. I screwed it directly into the tank in front of the cap.

vent2.jpg (69.41 KiB) Viewed 2216 times

you simply plug the old vent for good with a bolt and Loctite.

[handsomejackuk]

why do you need a tank vent ? My baghira has a locking petrol cap and has no vent tube on it, been working briliant ever since i have had it, i see no need for it !!!




Jak

[Bill Jurgenson]

I don't want to seem unduely pedantic:

My baghira has a locking petrol cap and has no vent tube on it

of course not. No stock tank has an external vent like that, not any more at least.
They are all internal.
That does not deter from the fact that the tank has to have a vent unless it is a pressure system not found on motorcycles.
It cannot work without a vent. It is as simple as that.
If yours works, fine. Leave it alone. Don't mess with a running system
The question was about Skorpions and tanks, tho, and there definitely can by problems there due to the materials involved in the vent, not its size as such.
Forget my one-off carbon fiber quickrelease racing cap ($$$); all stock bikes have locking tank caps unless the cap is under the seat. You can easily see the locking cap with the key inserted in the bottom picture further up.

Vent.jpg (68.68 KiB) Viewed 2135 times

Inside you see the vent tube going down to the base of the tank where a hose is screwed in from underneath. The large hole at the front under the cap is the vent. Any splash and also rain water to a certian extent (more theory than reality) are directed down thru the vent and not into the tank because of a slight ridge on the surface around the actual tank orifice.
Vents on old-type metal tanks are usually simply a hole in the cap itself. These tanks most often have a vent hose on top where additional venting is needed.

[handsomejackuk]

thanks for clarifying that i though my baghira does not need a vent. When i bought mine, it alreadyt had a locking petrol cap on it looks much better than the standard plastic one with a vent hose stickingout the top..

Really cleans up the top end of my bike.


Jak