Hello everyone. I am finally reassembling my 1980 xs400 special. Here is a question. On the bottom of the tank there is the tube that connects to the tap. Then there is a tube that goes to the other side of the tank. Is that tube supposed to connect to anything? Or is it just for a vent. The other part of the question is about the tube that runs from the tap to the carbeurator. My neighbor who worked on it and sold it to me put a balck tube on there. However gas just flows continuously to the carb. Do I need a different kind of tube. Or is there a way to turn off the fuel. Thanky you everyon, and have a good day!
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bcXS400-81
XS400 Enthusiast
The smaller diameter black tube that points towards the opposite side of the tank is a vacuum line that needs to be connected to one of the vacuum barbs on the carburator boots. The petcock is vacuum operated, so without that vacuum line hooked up I'm assuming fuel would free-flow, which is what you're experiencing right now. Also make sure your petcock isn't switched to prime, which allows free-flow of fuel as well.
jmd_forest
Bldg 1980 XS400 Cafe Bike
The vacuum tube from the carb boot to the petcock actually activates the petcock while the petock is in the RUN or RESERVE positions. The gas flows freely in the PRI position. The theory is that gas will not flow without the engine running and prevent carb overflow if/when the float valves stick open. The tube that runs from the petcock to the carb banjo bolt is the tube the gas flows thru.
The tube that goes to the carb inlet simply pulls the valve in the petcock open when the engine is running. The fuel always flows by gravity. On prime, the valve is held open with or without vacuum. Make sure whatever carb inlet you are are not using for the vacuum petcock is capped.
Thank you for the reply. Are you talking about the tube on the opposite side of the tank from the tap. If you are looking from the seat it woul be the right side of the tank. Sorry if I sound stupid, this is my 1st motorcycle. Where is it supposed to be connected? Not sure what you mean by carbeurator boot.
OliverB
XS400 Junkie
The "Carb Boot" is another term for the rubber intake manifold between the carb and the engine. At least one of the boots will have a nipple on it to which a vacuum hose from the back of the fuel tap is connected. If you mean that you actually have a tube or nipple coming out of the bottom right side of your tank, that is not stock and we don't know what to tell you about that. Need more info and a pic might help.
I'm sorry let me try to describe it better. I have a black tube that is connected to the tank on the same fitting as the tap. I ust funs across to the other side of the tank. Under the tank I have the fuel tap. From seat that is on left. Then there is a black tube that is connected to the tank and it goes to the opposite side of the tank from the fuel tap.So does that coonect to anything or is that just a vent type of tube? I really appreciate all your help. Sorry I'm not more knowledgeable.
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I gues maybel a better way of asking is if there is anything else from the tak that is connected to the carb besides the fuel tap, which is connected to the left carb (if you are lookin from seat). Thanks again.
Thr onr I am talkin about is connected to the same fitting on the tank as the petcock (or tap). It runs to the right side (from seat view). Where is it supposed to connect the the carb. I have the tube from the petcock (or tap) connected to the carb on left (from seat view). It is just a plain black tu (is that OK or is there supposed to be a bulb or something there. I am sorry I am not real knowlegeable. Thank you for your time.
....I just used these in another post, but here we go:
There is supposed to be a tube from the smaller barb on the petcock to a barb on the carb holder, which is this:
...and is located right here:
It only needs to be hooked up to one carb inlet, right or left, doesn't matter. However, whichever one you don't use, make sure you cap it so air cannot be drawn in.
There is supposed to be a tube from the smaller barb on the petcock to a barb on the carb holder, which is this:
...and is located right here:
It only needs to be hooked up to one carb inlet, right or left, doesn't matter. However, whichever one you don't use, make sure you cap it so air cannot be drawn in.
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