Topic: Tiny Carb fuel lines between the carbs questions

[jessezm]

Does anyone know if you can buy fuel line at the auto parts store or somewhere else local to replace the tiny lines between carbs 2&3 and 3&4 on a cb400f?  I think they're something like 2.5mm lines, and I'm too impatient to order a $0.40 part...  Thanks!!!

[Johnie]

I get my lines at the local hardware store or try NAPA, Autozone, etc. Best if you can take in a sample for size.

[MRieck]

You don't even need them

[Johnie]

Are you talking fuel lines or vent tubes? Starting to sound like the vent tubes now.

[jessezm]

On the microfiche it says fuel line, but I suppose I could be looking at the wrong part...  It's a black tube about an inch long and about 2.5mm (less than 1/8") diameter.

Somebody said you don't even need them--could that be true?

[Johnie]

Must be the ones I pictured below I am pointing at. You need those. Click the pic to enlarge...

[somesuch]

Must be the ones I pictured below I am pointing at. You need those. Click the pic to enlarge...

I have not tried running without on a CB750, but you do need bowl vent lines on the old GSXR 750 carbs. If you don't use them, cross winds totally screw up the carburation. One thing to note though, on CB750 carbs there are brass restrictors pressed in....so it may not matter if you don't use the lines. I do not remember GSXR carbs having restrictors, plus the lines are a lot bigger.

--Nick

[Bodi]

Possibly a small motor shop would have black. A hobby shop that sells R/C fuel engined car/boat/plane stuff will have the right size fuel line, theirs tends to be flourescent colours though.

[mystic_1]

In the stock configuration, the venting for the float bowls is done at the end of the long lines that come from between the center carbs and hang in the air.  The tube you're pointing to just connects the outer carbs to this system.  This configuration prevents water from being introduced into the float bowls when it rains, among other things.

Secondarily, since the pressure fluctuation in the bowls isn't enough to drive vapors all the way out of the hose when the pressure is positive, a fair amount of the fuel vapor stays in the hoses themselves and gets re-ingested when the pressure becomes negative, so it acts like a little emission control system   This effect is tiny though.


This is also where your fuel evaporates from when you leave your bike stored for 10 years with old gas in the tank and the petcock turned on, thus creating that brown varnish we all know and love inside your float chambers. 

mystic_1

[jessezm]

Nice, thanks everyone!  I'm brand-spankin' new to this forum, and it has been a HUGE help already!  I ended up finding some clear 3.2mm fuel line tubing that seems to have a good snug fit, although I did order the actual part from my local MC dealer.  I was impatient, though, and slapped the carbs back together tonight  I wish I had a before picture, cause they look so much better cleaned up.  I polished the bells and float bowls, and painted the rack black (I'll post pics when I get my build thread up and running).  Just for the record, if anyone is considering pulling their carbs off the rack for no apparent reason, plan on spending a solid evening or two scratching your head...

Tonight's work:  polishing rims, hubs, and triple tree!  (what else is a jew supposed to do on christmas eve?)