Carbs & Vaccum lines

[Anonymous]

I recently rebuilt the carbs and all went well, I noticed in my manual that there are hoses all over the place on the carbs. I do see the nipples between carbs 1and 2, 2 and 3, 3 and 4, but when I got the bike nothing was ever connected to any of them. The gas tank is vacumm dependent and I read that it should have a vacumm line going to it, but I have no where to connect any line but the fuel line (gas guage is taking another hose spot). Basically I'm just wondering how these need to be connected together or seperate and to where. If I didn't confuse anyone to much I'd appreciate any help.
P.S. Carb rebuild was fun and educational, not nearly as tough a project as I though it was going to be. I suppose the carbs are vm I'm not sure really, I do know that they look nothing like the ones illustrated in the carb rebuild series,, but are mikuni. 79' GS850

[frosty5011]

Hey there Walker,

Let me see if I can help. Being a '79, you should have the VM carbs, and originally, the carb setup probably had 8 hoses going from it. They would be as follows:

Fuel line......goes to the center "tee", between carbs #3 and #4

Vacuum line..... on pre-80 models, this is usually the fitting on top of carb #3 (to verify, look inside the throat of carb, engine side, and see if you can see a hole at the 2-3 o'clock position - something missing on the other 3 carbs).

Vent lines.....from the nipples coming off of carbs #2 and #4. These hoses are routed up over airbox and down the back.

Overflow lines.....4 hoses which are connected to the nipples on the bottom of the float bowls

[Anonymous]

Thanks, that's the set up but what do I do with the vacuum line on carb 3, where do I connect it, and the vents just route over the airbox (do I need to connect hoses to the vents at all as well as the overflows?) The vacuum on 3 is whats got me confused.

[frosty5011]

The vacuum line goes to the smaller nipple on the petcock. The petcock should have 2 nipples......the big one for the fuel line, and the smaller one for vacuum line.

If not using the original petcock, i.e. if you're using a Pingel......or some other one that is not vacuum-operated, then you can plug the vacuum line.

The 2 vent-lines, I really don't know if it will affect operation if there is no hose - it shouldn't, but I have read posts that say you should have the hoses/lines on there.

[Anonymous]

As for the two nipples off of the petcock well they are there one goes to fuel and the other is going to the fuel sending unit mounted to the underside of the tank, I don't know if this is correct that's how it was when I got it. I'll give pluging it a shot, I apperciat the help

[Don Lobacz]

The small nipple off the petcock is NOT supposed to connect to the fuel sending unit but rather to the nipple on the #3 carb. The fuel sending unit is run by the 2 wires - the nipple is simply for a drain tube that should go down behind the motor (so any gas leaks do not drip on a hot motor). The carb vent tubes are necessary so that the bowls have consistent atmospheric pressure above the gasoline. If you leave the hoses off, any water splashed there (rain or bike-washing) will go directly down into your carb bowls.

[Anonymous]

thanks fellas, you just helped clear things up a bunch, much appreciation, thanks.

[Anonymous]

Don's got it right. You know I had to figure all that out all by myself about 3 years ago. Would have been nice to have this kind of feedback then.