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'78 GS 1000 Carb Vent Hoses

  • Thread starter Thread starter Anonymous
  • Start date Start date
A

Anonymous

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Hey guys. I installed my carbs today and I am left with one vent hose. I do not know where it attaches to.

Imagine you're sitting astride the bike, with the fuel tank off. As you look down at the back of the carbs there are three vent hoses. The first one (left most) goes to the fuel guage foat assembly on the fuel tank. The next or center vent hose attaches to the fuel pet cock. Obviously the main fuel line goes to the fuel petcock as well. Which leaves the third (right most) vent hose. Where does this attach to???????????????
 
hoses

hoses

Hopefully someone with more info will step in here but I believe there are only two vent hoses both of which are between each pair of of carbs (1&2, 3&4), they terminate in the open, on the ground away from any source of heat in case you do have an overflow condition should your floats stick.
The middle hose attaches to the fuel petcock and is the supply for the carbs.
The other hose that you mention, the one from the float assembly, is a drain should the gasket fail for the float and should be routed to the same area as the two vent hoses....Mike
 
Mike - I'm QUITE certain that there are 3 vent hoses. If I were to route them all to the ground (as overflows) then that would leave the gas guage float mechanism and the petcock without vent tubes attached to them. Maybe we're talking about different carbs here. These are the original 26mm flat slides. please review my first post.


Anyone else got a clue?
 
mrblackjacksazook said:
Mike - I'm QUITE certain that there are 3 vent hoses. If I were to route them all to the ground (as overflows) then that would leave the gas guage float mechanism and the petcock without vent tubes attached to them. Maybe we're talking about different carbs here. These are the original 26mm flat slides. please review my first post.


Anyone else got a clue?
Click to expand...

the gas gauge one should go to the ground, as it's just an overflow for if it leaks internally, as should the 2 upper ones on the carbs,(they're breathers/vents) the 1 for the petcock is a VACUUM and should go on the tap on the #2 carb (forward side, top of throat), fuel line goes on carb fuel rail tap
 
The '78 GS1000 uses VM26SS carbs. There are two floatbowl vent tubes. One is between #1 and 2, the other between #3 and 4. They are routed under the seat or where they'll be in the clear and not kinked. The vacuum hose for the petcock connects to the left side of carb #3, it's about an inch above and an inch to the right of the fuel line. The gas tank gauge overflow tube routes down behind the left side cover (on my bike) and ends just below the swingarm so if the gauge gasket leaks, it will leak on the ground.
 
vacuum hose

vacuum hose

Forgot about the vacuum hose, replace my petcock with an aftermarket manual valve, I was close though :-)....Mike
 
So thats why my petcock only works on prime. After reading this i went out and looked at mine and all those vacuum outlets have caps on them. I guess i can now use a hose to goe to the petcock and it will work properly. Should i keep the other caps on them? I wonder if the prevoius owner had put those caps on there?
 
81 gs1100e has:
3 vent hoses (2 off the carbs (overflow) & 1 off the fuel level sender)
1 vacume hose for the petcock.
1 fuel line.
 
KEITH KRAUSE said:
The '78 GS1000 uses VM26SS carbs. There are two floatbowl vent tubes. One is between #1 and 2, the other between #3 and 4. They are routed under the seat or where they'll be in the clear and not kinked. The vacuum hose for the petcock connects to the left side of carb #3, it's about an inch above and an inch to the right of the fuel line. The gas tank gauge overflow tube routes down behind the left side cover (on my bike) and ends just below the swingarm so if the gauge gasket leaks, it will leak on the ground.
Click to expand...

79 GS1000N has hoses setup actually the same.
 
gs1000dude said:
So thats why my petcock only works on prime. After reading this i went out and looked at mine and all those vacuum outlets have caps on them. I guess i can now use a hose to goe to the petcock and it will work properly. Should i keep the other caps on them? I wonder if the prevoius owner had put those caps on there?
Click to expand...
If you have the VM carbs, '78/'79 GS1000, the brass nipple coming off the left side of carb #3 is for your vacuum. The other two, coming off the left sides of #2 and #4 are for venting the floatbowls. These two should not be capped. Capping will cause fuel starvation, most noticable at constant cruising speed.
 
'79 GS1000

So, if I am understanding correctly, sitting on the bike, tank off, looking at the carbs:

4 hoses. Bigger diameter hose is main feed line, middle hose is vacuum supply line, and the 2 outermost hoses are vent tubes right?

If one were to fashion a crude gas feed, would he attach it to the thick hose or would he need to attach it to the center hose as well? (the reason I ask is my gas tank has a million little rust holes in it and won't hold any fuel, and I'm trying to get this bike running while I wait on my new tank to show up).
 
If you are using something like a lawn mower gas tank just cap off the vacume line that would normally run to the petcock, and hook the normal gas line to it.
 
Psychoholic said:
'79 GS1000

So, if I am understanding correctly, sitting on the bike, tank off, looking at the carbs:

4 hoses. Bigger diameter hose is main feed line, middle hose is vacuum supply line, and the 2 outermost hoses are vent tubes right?

If one were to fashion a crude gas feed, would he attach it to the thick hose or would he need to attach it to the center hose as well? (the reason I ask is my gas tank has a million little rust holes in it and won't hold any fuel, and I'm trying to get this bike running while I wait on my new tank to show up).
Click to expand...
Yes, you have the 4 hoses right.
If you hook up a temporary gas source, the fuel will go to the "T" fitting (the largest hose). This needs to be 5/16" I.D. I would buy a longer length of new hose and not bother with connecting two hoses.
Then cap off the vacuum nipple on the left side of carb #3.
Be sure your temporary gas source is vented too.
 
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