Topic: Air in Fuel Lines

[mlinder]

So, I got some new fuel lines.
Clear.

Big sections of air.  Fuel seems to 'go around' these bubbles. Always fuel right above the T Joints, about 1.5 inches.
Air bad in the fuel lines?
I would think so....

Any thoughts?

[Bodi]

Bubbles won't cause trouble, they just float up to the high spot as fuel flows past them. If there was enough fuel flow to cause a problem they'd just get pushed through to the carbs and be gone.

[TwoTired]

With a full tank of fuel and good head pressure, the gas will likely travel around the bubbles.  It is when the tank is low on fuel and there is low head pressure that the bubble's boyancy may cancel or interfere with gravity pulling the fuel where needed.

It is best to arrange the fuel line for a constant fall, source to destination, as any plumber would run a water drain line dependent on gravity for flow.

Cheers,

[mlinder]

With a full tank of fuel and good head pressure, the gas will likely travel around the bubbles.  It is when the tank is low on fuel and there is low head pressure that the bubble's boyancy may cancel or interfere with gravity pulling the fuel where needed.

It is best to arrange the fuel line for a constant fall, source to destination, as any plumber would run a water drain line dependent on gravity for flow.

Cheers,

Yeah, I'd love to, but pretty much impossible with this.
The bottom of the petcock nipple is literally 2 inches above the top of the T-joint nipple. Having to travel over the Choke Linkage, etc, puts the upper loop above the bottom of the petcock nipples.
On the right side, the petcock nipple is abou 4 inches away from the right bank T-joint nipple.
On the left, its quite a bit further, but has to travel OVER the breather hose in order to not foul the choke linkage.
I might just have ot get a mouthful of gas and get those bubbles out.
THey may not 'hurt' anything, but they bug the crap out of me now that I can see them.

[Bodi]

Drain the bowls, open the gas cap and seal your face over the opening to blow as hard as you can and pressurize the tank, then open the petcock. The high rate of fuel flow might push the bubbles through. Then avoid running out of gas!
Or get black fuel line so you don't see them

[TwoTired]

I might just have ot get a mouthful of gas and get those bubbles out.

Ew, don't do that.  I splurged some time ago and bought a Mity-vac.  Jeez, I use that thing a lot.  One of the best return on investments I've made for the shop.

If not that route, be clever and make gravity your friend.  Is it possible to "walk" or wave the bubble back to the petcock?  I'm sorry to say though, that it will likely be temporary, as an air source is the float valve sitting in the air chamber above the float bowl fuel.

Hard to believe Honda would have forced such a routing.  But, I've not encountered an early 750, either.  Well, besides group 6 of the Honda Shop manual.

Cheers,

[jtb]

Or get black fuel line so you don't see them

I'm with Bodi on this one.

I really had to bite my tongue to keep from saying nipples.  Ooops...

[paulages]

mark-- i usually use a pair of needle nose pliers, and loosen the lines at the petcock just enough for the air to escape and fuel to fill the void. run out of gas, and you'll be doing it again...

[750duo]

With a full tank of fuel and good head pressure, the gas will likely travel around the bubbles. It is when the tank is low on fuel and there is low head pressure that the bubble's boyancy may cancel or interfere with gravity pulling the fuel where needed.

It is best to arrange the fuel line for a constant fall, source to destination, as any plumber would run a water drain line dependent on gravity for flow.

Cheers,

Drain the bowls, open the gas cap and seal your face over the opening to blow as hard as you can and pressurize the tank, then open the petcock. The high rate of fuel flow might push the bubbles through. Then avoid running out of gas!
Or get black fuel line so you don't see them

Ew, don't do that.  I splurged some time ago and bought a Mity-vac.  Jeez, I use that thing a lot.  One of the best return on investments I've made for the shop.

If not that route, be clever and make gravity your friend.  Is it possible to "walk" or wave the bubble back to the petcock?  I'm sorry to say though, that it will likely be temporary, as an air source is the float valve sitting in the air chamber above the float bowl fuel.

Hard to believe Honda would have forced such a routing.  But, I've not encountered an early 750, either.  Well, besides group 6 of the Honda Shop manual.

Cheers,

mlinder

All very good suggestions: however  

Why not just raise the gas tank about 4 inches. You could do this by making a small tray of aluminum and sliding it under the tank and mounted on the upper tube of the frame. This would also allow you the luxury of a GLOVE BOX under the tank- just like the "gold-wing" guys!!!? Maybe install twotired's Mity-vac under the gas cap.  

Alternatively, you could install larger diameter rims/tires and then lower the engine - uh - maybe not?
probably would have the rake the front forks too.  

   Seriously though, I think most of us have had this problem and solved it by routing the gas lines as best we can, keeping the tank pretty full, and in my case - using the "black" tubing so I can't see the possible bubbles - and therefore just roll the throttle on and chomp the bugs.  

Luck

Tom
 

[merc2dogs]

 I've been running clear line almost forever it seems, always replace old black rubber line with clear on the first tune up on every bike I get unless the line looks like brand new.

 I always run my lines 'wrong' according to most people, which is straight down under the carbs, then over to the nipples (74 750)  does give a straight upward run for the bubbles to get back into the tank and out of the line

 The girls hondamatic I hooked up same as it was and it ALWAYS has a big bubble an inch away from the petcock.

Ken.

[mlinder]

Good ideas (and the ones that weren't good were at least funny).