Do These Hoses Connect To Each Other?

[Quasikaze]

Hey Guys,

I'm new to mechanical work and I'm restoring a 1980 Yamaha XS 650 SG as a hobby project to learn. I've gone through and cleaned the carbs, changed the oil, replaced the battery, and next is cleaning the fuel tank.

The issue I'm having is that I have two hoses that are disconnected. Here are a couple of pictures https://sli.mg/a/bcsUt5 . I've circled the respective hoses with red and yellow. If I remember correctly, they were disconnected when I got the bike. I just want to make sure I have it right in my mind before I just start connecting stuff. I'd rather not clean the fuel tank until I know what it connects to.

Also, why are there two hoses? Is there supposed to be something between them, connecting them together? Why not just one hose that goes straight from the tank to the carbs?


Edit: Side note - If there are any good tutorials on this site that I should definitely take a look at, then I'm completely open to advice.

SOLUTION: They do NOT connect together. The line from the carbs connects into the back of the petcock, and the line from the petcock connects to the small nipple below it on the manifold.

 

[weekendrider]

Red is fuel line from petcock to carbs. Replace it with new.
The yellow is the vacuum line from intake to petcock.
It pulls a vacuum on the diaphragm in the petcock to allow fuel to flow through.
You want to read the carb guide. From the toolbar click tech follow the menu to carbs.

 

[5twins]

You have a vacuum powered petcock. That's why there are two hoses attached to it. The smaller one feeds a vacuum signal in to operate the petcock (turn it on and off). The larger line feeds fuel out to the carbs. The vacuum supply nipple is shown in your first pic, to the right of the yellow circled vacuum hose end. Plug the hose onto that nipple. The other intake manifold should have a nipple as well. Make sure you cap that one or you will have a massive air leak.

 

[gggGary]

Plan on a petcock rebuild or replacement, don't even think about putting a fuel line to the carbs until you KNOW the petcock is working properly. As always only NEW fuel line. BS34 carbs must have the float valve o-rings replaced. If you don't do all this your next thread will be titled "Why is fuel pouring out of my LH carb inlet?"

 

[5twins]

You wanted a hobby, you've got one, lol. The 650 is an excellent bike to learn on, very easy to work on. Being as old as it is, and most being somewhat neglected, there will be lots to do. Pretty much all of it is outlined on the site here somewhere. A pic to help with the carb hose connections .....

Vacuum line (orange hose) comes off the front of the petcock and connects to the nipple on the intake manifold. Fuel line runs off the back of the petcock to the carbs.

 

[Quasikaze]

Thanks for the all the help, guys! I'll certainly check out the carb guide. I've actually bookmarked the page with all the links on it. With y'alls help, I was able to figure out where they connect. I'll make sure to grab a petcock rebuild kit. I haven't cranked it yet. I've been waiting until I got all the major stuff done.

How do I figure out what model my carbs are? I see where it says "Mikuna" on them. Do I need to take them off and find a model engraving/sticker somewhere on it?

 

[gggGary]

They are BS34 appear to be the 1980 brass float model. Do a HOT water dip test of the floats; microwave a cup of water til hot hold the float with a pliers dip in the water for a couple seconds, a small stream of bubbles = fail.

 

[650Skull]

Not sure its an 80, the rocker cover looks to be factory black making it an 81. Plastic float BS34's

Not to take away from, testing brass floats.

 

[Quasikaze]

I called Yamaha a while back to verify the vin and they said it was an 80. Is it possible those are aftermarket, though to be honest, I'm not sure what a "tappet cover" is yet.

 

[gggGary]

Not sure its an 80, the tappet cover looks to be factory black making it an 81. Plastic float BS34's

Not to take away from, testing brass floats.

I went from the carb pic, the float drains are the straight down threaded plug style not the side screw and nipple for a drain line type. AFAIK those bowls have brass floats inside, at least as delivered. Foam floats can be swapped in. He also stated he had an 80. On the engine paint; keep looking, the bike frame is painted metallic blue and some of the black is flaking off the cam cover. The factory black usually just fades away to grey aluminum instead of flaking off

 

[XSLeo]

Tappet cover or valve adjustment cover. There are four of them. Two on the front of the engine are exhaust valve adjuster covers, one is square and has for bolts, the other triangular and three bolts. Two one the rear are intake, both triangular and three bolts.
You remove these covers to adjust the valve clearances.
The procedure is in your repair manual.
This is step two in the tune up procedure, step one is cam chain tension. step three is timing check.
Then onto carbs.
Leo

 

[650Skull]

I did say tappet cover, I should have said Rocker cover. Corrected last post