Fuel Tanks: Interchangeable?

[mixelpix]

Hi,
I just got my first 1979 XS 1100 Special. Rode it down from Eugene, OR to Oakland, CA. Awesome bike! I was, however, a little frustrated with the fuel capacity of the tank. Are the standard tanks (which hold more) interchangeable with the specials? Any thoughts on swapping them out would be appreciated - especially regarding the fuel indicator and the possibility of having the same lock for both the tank and the ignition. THANKS!

[Do Lee]

Mixelplix,
Yes the tanks are interchangeable I also have a 79SF I have replace the special tank with a standard tank. (78-80 model)
If you are contemplating on swapping tanks here are a few things you need to know.
1. The fuel petcocks are not interchangeable as well as the gas cap.
2. The seat will fit with the standard tank but you have to force it into place. I experimented on my donor bike seat pan by adding an aluminum extention on the front tab so the front end of the seat would be secure under the gas tank.
3. The Special (bike) uses the octopus system, one diaphragm ass'y to distribute the fuel to the carbs. The Standard (bike) has the diaphragm on each fuel petcock so you will need to rework the fuel lines for this difference. I removed my octupus fuel system and reworked the fuel lines like that of the Standard models and added in-line fuel filters.
4. Make sure that you install the drain line from the drain nipple, this allows fuel or water to drain from around the fuel gas cap area to the ground and not on the bike seat and battery area.
So if you buy a standard tank, try to buy a complete tank system.
If you can't buy a complete tank system you will need to also get gas cap and filler cover, fuel petcocks, the fuel sender unit can be used form your special tank. I know that the fuel light never comes on at the same time to indicate needing to refuel, usually around the 1.5 to 2.5 gallons remaining . I go by mileage 33-35mpg
These are a few things that I came across with my tank change out.

Do'lee

[mixelpix]

Thanks - I was a little aprehensive about just buying one to find out. This helps enormously!

[mixelpix]

I am having trouble finding any reference on how the standards make the connection from the petcocks to the carbs. Is there anything tricky to the standards, or do they simply connect one hose to two carbs on each side?

Would there be any reason not to swap the standard petcocks out for the specials and keep the octopus? I believe the only difference is the height of the reservoir. Only reason I ask is that I have found a standard tank with the fuel send, cap/keys but no petcocks.

Thanks!
-pdk

[John]

The Standard and Special fuel delivery systems are two seperate animals, and cannot interbreed.
The petcocks will not interchange from a Standard tank to the Special, or vice versa. They are different sizes. The petcocks on a standard are vacuum actuated, and the Special has manual pecocks and the Octopus is actually the vacuum actuated fuel shut off/ distribution valve. The Standard uses one petcok to feed one set of carbs. i.e. the left side petcock feeds # 1 & 2 carbs, and the right side petcock feeds # 3 & 4 carbs. If you have a Standard tank, then you must have Standard petcocks.

[Dennyz]

I have successfully changed the lock in a fuel cap. The tank, side cover, and helmet locks have the same lock mechanism. I took the lock out of a helmet lock and put it in a gas cap.