79 gs750 fuel/vaccum lines

[MTHughes]

Hello all, I just found this site today and already it has been more info i have found anywhere else, it's awesome. So here is the story/problems. I bought a 79 gs750 about a month ago with was pretty much in parts. I started putting everything back together and in the process rebuilt the carbs. Now since I didn't take all the original lines and hoses off I don't know where they all go. From searching on here I have read where all the lines and hoses are supposed to go. The main fuel line out of the petcock goes to the T in between the 2 & 3 carbs, the outlets at the bottom of each carb are for overflow lines. The two nipples in the middle of carbs 2 & 4 are to air lines and get routed toward the rear of the bike. Now here is the problem, I don't have the middle nipple on my #3 carb that is supposed to be routed to the smaller line coming off the petcock. I don't know if they were rebuilt previously and let's say what should be a #1 carb was put into where #3 should be or what. I don't know if this is normal and I am just misunderstanding something or what is going on.
Also a couple other points I'm not totally clear on. Where does the third hose coming out of the gas tank go, on the opposite side of the petcock, and what diameter is the fuel line cause that was missing in the part box I got from the previous owner. Thanks a ton and awesome website, I will definately be here almost everyday!!

Mike Hughes

[doctorgonzo]

On my 1000 (and should be the same) the vacuum hose connects beteeen 1 and 2.

[Greg O.]

Hey Mike,


Welcome to this place. There is a world of knowledge here about GS bikes, and it has been very helpful as well as fun reading and posting here.

I have a 1979 GS 750L, and I am pretty sure the vacuum comes off #3 carb on mine. If you can get the bike to start, you will find out soon enough which one it is by placing a finger over the each of the nipples on the carbs. I use a lawnmower gas tank to run mine on when I have the gas tank off. This works good for synching the carbs.

Is your 750 an E, or L?

Greg O.

[Greg O.]

I just re-read your post, and I don't think you can interchange #1 and #3 because the center carbs have a flow trough from one side to the other for gas to flow to the outer carbs 1 and 4. Did they mix up 2 and 3 by chance? I don't know if that is possible without looking. Or did they pull a used carb off another bike, and do away with the vacuum petcock?

Keep us posted what you find out.

Greg O.

[pbdavey]

GS650EX here....I think we all have Mikuni BS32 and I'm in the middle of my rebuild. The vacuum on mine is off #2, iirc (right beside the air screw). Also, Greg O. is right, you can't mix any of the carb bodies. #2 has the vacuum, #1 and #4 have closed off fuel troughs on different sides, and #3 has neither the vacuum nor the closed troughs.
Look yourself, but I _think_ this is correct information.