XS750 fuel lines - 2 on each petcock?

[mikewerx]

So getting this XS750 back together, and can't remember why there are 2 ports on each petcock..? the bottom ones obviously go down to the carbs, but what are the top 2 nipples for? Where do these hoses go? They are smaller then a 1/4" hose will fit, so assuming vacuum lines? Thanks for the help!

 

[Wahoo650]

The one on the back side is not a fuel line- it's the vacuum line. These are vacuum operated, ment to only allow fuel flow when there is vacuum present- ie the engine is turning. The source is the spigots off of #1 & #3 cylinder at the intake. The diaphrams tend to fail with age and may allow fule to run all the time. They may also allow fuel to run thru the vacuum port directly into the cylinder. When this happens, the fuel will seep past the rings and contaminate the oil- very bad for the bottom end! This is referred to as "gas-oil" not a good lubricant. Check out the triples site. Some very good info. there for a Yamaha triples novice.

http://www.yamaha-triples.org/portal.asp

Matt

 

[mikewerx]

Thanks Matt, So would it be safe to just cap these off, and not use them?

Yeah, been a member at the triples site for a while, and pretty bare bones, not a ton of info there, but there is some ... thanks.

 

[Wahoo650]

If you just cap them off they will only let fuel through in "prime". Must have vacuum to work unless modified. I replaced mine with a set of manual valves from MikesXS.