Your fuel is disappearing. Capture it.


41 replies to this topic
  • cornelieaz

Posted April 07, 2008 - 04:52 PM

#1

Here's a write-up with pictures of something I rigged up on my bike that you may find very useful.
http://www.thumperta...264#post6191264

  • Bibleman

Posted April 07, 2008 - 05:34 PM

#2

Good thinking! I may do that myself:prof:

  • Blacksamwell

Posted April 08, 2008 - 05:43 AM

#3

Are you leaving the float drain open or closed? I'm having trouble visualizing how your tank will now relieve any vacuum created if the vent tube is attached to a closed float drain nipple. If the drain is open, wouldn't that mess with the gas level in the float bowl?

  • ghrati ghoti

Posted April 08, 2008 - 06:41 AM

#4

Are you leaving the float drain open or closed? I'm having trouble visualizing how your tank will now relieve any vacuum created if the vent tube is attached to a closed float drain nipple. If the drain is open, wouldn't that mess with the gas level in the float bowl?


You are correct, that is the bowl drain. There is a screw opposite the view in the pictures.

  • cornelieaz

Posted April 08, 2008 - 08:02 AM

#5

Are you leaving the float drain open or closed? I'm having trouble visualizing how your tank will now relieve any vacuum created if the vent tube is attached to a closed float drain nipple. If the drain is open, wouldn't that mess with the gas level in the float bowl?


The drain is open. As the tank vents fumes out into the line, the fumes condense back into liquid fuel as opposed to being lost into the atmosphere. When the level of fuel rises in the carb bowl because of this effect, the fuel (in liquid form now) will drip back into the line, underneath the carb, and wait there to be re-used when the either the bike fires back up, or the tank creates a vacuum and pulls it back in.

It works great. Tested and tested again. Not only is it a gas saving, eco-smart upgrade, it's also fun having and watching what feels like a science lab going on all the time.

  • xr650l bum

Posted April 08, 2008 - 08:06 AM

#6

How does the tank breathe? If you have a closed system dont you have a problem with the fuel not draining out of the tank?

  • ghrati ghoti

Posted April 08, 2008 - 08:24 AM

#7

The drain is open. As the tank vents fumes out into the line, the fumes condense back into liquid fuel as opposed to being lost into the atmosphere. When the level of fuel rises in the carb bowl because of this effect, the fuel (in liquid form now) will drip back into the line, underneath the carb, and wait there to be re-used when the either the bike fires back up, or the tank creates a vacuum and pulls it back in.

It works great. Tested and tested again. Not only is it a gas saving, eco-smart upgrade, it's also fun having and watching what feels like a science lab going on all the time.


Do you have a feel for how much gas evaporates? I have a vent valve thingy on my cap. Every once in a while I get a wiff, but not always.

  • cornelieaz

Posted April 08, 2008 - 08:28 AM

#8

How does the tank breathe? If you have a closed system dont you have a problem with the fuel not draining out of the tank?


Liquid is more dense than vapors, so when the tank vents, it vents in vapor form. It then condenses to liquid form in the line allowing for more vapors to escape...I imagine that's how it works most of the time. In the event that the tank is venting too fast to allow that change to take place, it just vents the vapors out through the jets like the carb bowl always does anyway.

  • xr650l bum

Posted April 08, 2008 - 08:33 AM

#9

To help with the gas evaporating, I put heat shield tape on the bottom of the tank. This help with boiling the fuel away.

The tank needs to draw air in, to allow the fuel to flow. How does your system allow this to happen?

  • cornelieaz

Posted April 08, 2008 - 08:43 AM

#10

Do you have a feel for how much gas evaporates? I have a vent valve thingy on my cap. Every once in a while I get a wiff, but not always.


Yeah, that's exactly how mine worked too. Depending on the current temp/riding conditions, the tank may be venting in or out. If you get down to the side and look across the tank cap on a sunny day though, you'll see the vapors pouring out like a mirage.

It's a little tough to measure the amount...here's why: When the tank temp is rising, it vents into the line, when it cools, it pulls back in, so much of your evaporated fuel will get sucked back into the tank making a visual inspection at any given time kinda inaccurate. The beauty of it though, is that when it's venting out, it's spitting out evaporated gas. With this rig, when it's venting in, it's no longer just pulling in dry air, it's pulling in very fuel rich vapors...just like the ones it lost initially.

That said, the six inches or so of line under the carb will fill with liquid fuel in 30min after every ride.

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  • cornelieaz

Posted April 08, 2008 - 08:55 AM

#11

To help with the gas evaporating, I put heat shield tape on the bottom of the tank. This help with boiling the fuel away.

The tank needs to draw air in, to allow the fuel to flow. How does your system allow this to happen?


When it needs to pull air in, it pulls it down through the jets, accross the carb bowl, through the bits of fuel in the line, and back into the tank. The speed at which it pulls air in is EXTREMELY slow...if at all. When running, the pressure in the tank increases from engine temp and sloshing around at the same time that the fuel level is dropping, making venting a very small factor. The air/gas mix is not significantly effected since the rate at which the tank vents (in either direction) when running is FAR less than the rate at which the engine eats gas.

  • ghrati ghoti

Posted April 08, 2008 - 09:10 AM

#12

Yeah, that's exactly how mine worked too. Depending on the current temp/riding conditions, the tank may be venting in or out. If you get down to the side and look across the tank cap on a sunny day though, you'll see the vapors pouring out like a mirage.

It's a little tough to measure the amount...here's why: When the tank temp is rising, it vents into the line, when it cools, it pulls back in, so much of your evaporated fuel will get sucked back into the tank making a visual inspection at any given time kinda inaccurate. The beauty of it though, is that when it's venting out, it's spitting out evaporated gas. With this rig, when it's venting in, it's no longer just pulling in dry air, it's pulling in very fuel rich vapors...just like the ones it lost initially.

That said, the six inches or so of line under the carb will fill with liquid fuel in 30min after every ride.


The way you measure float height is by attaching a hose like that and hold it next to the bowl. The fuel in the hose will be level with the fuel in the bowl.

  • cornelieaz

Posted April 08, 2008 - 09:30 AM

#13

The way you measure float height is by attaching a hose like that and hold it next to the bowl. The fuel in the hose will be level with the fuel in the bowl.


Not the case. The fuel in the line doesn't even rise to the bottom of the carb bowl itself, let alone to the top of the bowl level. Refer to the picture of fuel collecting in the line.

  • Denn10

Posted April 08, 2008 - 01:42 PM

#14

why not just put a check valve on your breather from your tank? I dont see how you ride with your bowl drain open, that doesnt make any sense in how you explained it???? I have never had a bike that i could just see fuel evaporating out of the tank just sitting and looking at it?? ALSO dont you realize with a plastic tank you have vapors just seeping thru the plastic tank all the time anyways? i doubt your saving any fuel doing this as your losing it thru the plastic anyways.

  • XR650L_Dave

Posted April 08, 2008 - 01:53 PM

#15

Not the case. The fuel in the line doesn't even rise to the bottom of the carb bowl itself, let alone to the top of the bowl level. Refer to the picture of fuel collecting in the line.


If the bowl drain is open, this must mean there is actually a little bit of pressure in the line holding the fuel up and out of the line (the opening in the drain is probably small enough to allow the sir to remain trapped on the bottom).

As long as you don't end up pushing a bunch of extra fuel up into the bowl and causing it to flood, this looks pretty good to me.

Keep us updated.


Dave

  • cornelieaz

Posted April 08, 2008 - 05:34 PM

#16

why not just put a check valve on your breather from your tank? I dont see how you ride with your bowl drain open, that doesnt make any sense in how you explained it???? I have never had a bike that i could just see fuel evaporating out of the tank just sitting and looking at it?? ALSO dont you realize with a plastic tank you have vapors just seeping thru the plastic tank all the time anyways? i doubt your saving any fuel doing this as your losing it thru the plastic anyways.


A check valve would only allow flow in one direction...the tank breathes in and out. It also does nothing to stop evaporation.

To my knowledge, the "drain" doesn't open into of the bottom of the bowl, it's an overflow port from out the top of the bowl to prevent flooding into the engine when the bike is tipped. I could be wrong, however, this port was open and breathing before this rig which would suggest that it's not simply a drain like the plug on an oil pan.

Fuel vapors are transparent, and are only visable much like heat waves rising from the hood of a car on a hot day.

The Clarke poly-ethylene tanks do bleed through. However, my tank is vapor sealed with a non-gas permeable coating compliments of Johnson's Future Wax.

I know it makes the brain go :thumbsup: but it works....quite well. When my bike blows up and you all get to point and laugh, I'll let you know.

  • XR650L_Dave

Posted April 09, 2008 - 09:10 AM

#17

Do you have the drain screw open, or closed?


Dave

  • DGXR

Posted April 09, 2008 - 09:24 AM

#18

To my knowledge, the "drain" doesn't open into of the bottom of the bowl, it's an overflow port from out the top of the bowl to prevent flooding into the engine when the bike is tipped. I could be wrong, however, this port was open and breathing before this rig which would suggest that it's not simply a drain like the plug on an oil pan.


This is what had me confused this whole time - what you are calling a carburetor bowl drain is not a drain at all. You are connecting the fuel tank cap vent line to the carburetor overflow. Let me know if I'm way off but this is what I've gathered from both threads, at least now it makes sense to me. A friend and I got kinda excited about this idea and we will see how it works on our bikes (he's got a DR-Z 250). For $3 worth of fuel line, it would be cool to save fuel vapors from escaping and keep them in my bike. Save me money (over the very long run), save some air quality! :thumbsup:

  • jetfuel

Posted April 09, 2008 - 09:48 AM

#19

You still have fuel evaporating out through the main and pilot jets back through the airbox.

I would think the fuel your going to recover is very minute, probably less than the amount I see people splashing down the sides of thier cars at fill up.

But hey, if it makes you feel better thats cool..:thumbsup:

  • ghrati ghoti

Posted April 09, 2008 - 09:56 AM

#20

A check valve would only allow flow in one direction...the tank breathes in and out. It also does nothing to stop evaporation.

To my knowledge, the "drain" doesn't open into of the bottom of the bowl, it's an overflow port from out the top of the bowl to prevent flooding into the engine when the bike is tipped. I could be wrong, however, this port was open and breathing before this rig which would suggest that it's not simply a drain like the plug on an oil pan.

Fuel vapors are transparent, and are only visable much like heat waves rising from the hood of a car on a hot day.

The Clarke poly-ethylene tanks do bleed through. However, my tank is vapor sealed with a non-gas permeable coating compliments of Johnson's Future Wax.

I know it makes the brain go :thumbsup: but it works....quite well. When my bike blows up and you all get to point and laugh, I'll let you know.


It is a bowl drain on a stock CV. :thumbsup:





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