Vacuum line questions...

Why is the vacuum line attached to the #2 carb? Is it possible to connect it to any of the others?
And when I was out looking at bikes I saw a yamaha xj750 (almost 60k on the odometer) with a vacuum line on #2 and #3. The person used a splitter. What does that do?

 

it doesn't matter which intake boot - mine's on #3.

can't speak for the splitter.

 

Skeeter is right, the vacuum line is required for your petcock and it doesn't matter which carb it's on.

As for the splitter, I've heard some try to achieve some sort of balancing between the carbs (almost like a YICS) - personally, I don't buy it. Your friend may be trying to achieve vacuum during all strokes of the engine. Not sure it matters though.

 

now that i've thought about it - it does kinda matter where you hook up the vacuum line. if it's too short, you can't hook it up to #4.

also - watch the routing of the vac line if it's hooked up to #3 or #4 - i noticed the PO had ran the line right across the throttle cable, so the cable was slowly sawing it's way through the hose. if memory serves, WOT would actually pinch the vac hose, too.

 

It came connected to #2 on the 550s and #3 on most of the bigger bikes. From looking at my 650, I have NO foggy reason why they ran it all the way over to #3 instead of #2. Two is closer, and on the 650 Seca at least, there seems to be no reason to have gone to #3.

Gotta be careful moving it; on some bikes (don't remember which) the carb with the vacuum line is jetted differently. Mighta been the XJ600 but I don't recall...

 

Well i am not going to do the splitty thing. Just curious. And my reasoning for wanting to know about moving the line to a different carb is I have a leak in #2 rubber and don't want to fix it. Just kidding. Small split in the new vacuum line and want to just cut off the tip and be done with it. It'll be a little shorter so was just going to go to 1. As far as the split line, it was at a dealer and come to think of it Fraps reminded me of other attempts at trying to creat the YICS affect on other bike by connecting the manifold rubbers. Maybe it was someones attempt in a different way. i almost want to try it. Just learning, in depth, how these carbs work. If you want to be extremely bored but get extremely useful info, google "how cv carburetors work". haha. Dammit Fitz, you Carb guru. When i grow up I'm gonna be just like you. Oh... and by the way, all you 550 guys out there... we got damn lucky with yamaha's decision to use the Mikuni carbs. From what I am reading they are actually high end and top knotch carbs. If my 550 goes to hell, I am keeping mine.

 

would it stand to reason that longer the vacuum line, the smoother the "pulse" seen by the petcock? maybe that's why they run it all the way to #3?

 

Maybe but mine is run to #2 at the moment.