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Old 11-15-2012, 09:49 PM   #1
Myfuture_yourdebt OP
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in-tank hoses with gravity fed carb

Looking for some thoughts, advice, experiences in a similar vein...

The position of the factory fuel valve/petcock on my KLR650's gas tank leaves a fair amount of fuel below it in the lowest portions of the tank, never to be touched since it can't even be drained unless you were to remove the tank, open the cap and turn the tank upside down. The bike is, of course, a gravity feed carbed bike with no fuel pump. I have a new, larger plastic tank which I'm going to install soon. The unuseable fuel in this tank will be even greater if I re-use the factory petcock without any modifications.

The petcock is a simple fuel valve, a tube-like screen and a brass tube with the same kind of screen on the end of it creating the reserve and main fuel intake sources, respectively. My idea is a take on Skip Faulkner's fuel tank mod...I'm thinking of giving this a whirl:

Cut out "reserve" screen of petcock
Remove main brass intake tube (it's only press fit)
Cut it down to only an inch or so in length and bend it slightly if possible
Put this tube into the reserve intake position with the bend facing towards the front of the tank
Connect a ~12" long piece of Tygon fuel tubing to petcock
Insert petcock and tubing into tank
Fish out tubing from the cap opening, then attach a barbed in-tank style fuel filter to the end
Position fuel filter as low in the tank as possible with as horizontal angle as possible from filter to petcock
[This filter-to-tubing-to-tube intake would be the new "reserve", hence putting the tube in the reserve position on the petcock]
Install an in-line fuel filter post petcock since the new reserve fuel intake on the petcock would be without any screen

My main concern is that this in-tank "reserve" tubing won't be able to siphon fuel upwards at all...making this modification a total waste of time. If it is able to siphon fuel to the petcock, I wonder if it'll cause fuel starvation because the flow isn't sufficient.

And now I'm all ears

Myfuture_yourdebt screwed with this post 11-15-2012 at 10:01 PM
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Old 11-15-2012, 11:21 PM   #2
GreaseMonkey
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Does your valve look like this:




If so, you can probably just remove the filter screen on the reserve, push a section of hose (I'd give it a dab of epoxy too) over the tube, then get another small section of tubing that you can put into the other end of the hose and glue the screen back on and reinstall. I'd leave the original intake tube the way it is, no need to fiddle with it.
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Old 11-16-2012, 05:54 AM   #3
CycleDoc59
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I believe this is what you are looking for:

http://www.bigcee.com/faq/fuelmod.html
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Old 11-16-2012, 09:14 AM   #4
Myfuture_yourdebt OP
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Yes my fuel valve looks like that. There is no tube for the reserve, just the screen.

Obviously I've already looked at the poorly written Skip Faulkner fuel tank mod quite a bit, hence giving him credit in my OP.
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Old 11-16-2012, 03:31 PM   #5
Ranger Ron
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I have an Acerbis fuel tank on my 2006 KLX250S. It has wings similar to the KLR tank that extend well below the carburetor inlet.

To get at all the fuel, I did something like what you are contemplating with the exception that I used a snowmobile fuel pump. They are vacuum operated. The system worked perfectly (for a while).

Tygon tubing was the issue. It is formulated for gasoline, but I didn't realize at the time that it isn't formulated for alcohol. After a few months, the tubing swelled up and the brass barbs (weights) on the ends of the tubes fell off. Actually, only one did, but that was enough.

I returned the system to stock for a while then decided to redo it with Viton tubing. That worked, but now there was another issue. The KLX is my secondary bike and it sometimes sits for several weeks before being ridden. I always drain the float bowl if the bike is not going to be ridden for some time. In order to get gas into the carburetor, the bike has to crank for a very long time. The fuel pump doesn't have a high volume flow. I would find that I would sometimes exhaust the battery before the float bowl would fill and the bike would start.

Obviously, if the bike were ridden regularly, that wouldn't be a problem.

So, once again, I returned the bike to "standard" mode. Surprisingly, I've found I can use fuel in the wings well below the carb input level. The Acerbis tank has a center well where the petcock is. I guess just normal fuel sloshing fills this well from the wings.

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Old 11-16-2012, 04:10 PM   #6
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What kind of Tygon tubing did you use? "Tygon® F-4040-A Fuel & Oil Tubing"? It's suppose to be resistant to swelling and resistant to gasoline/alcohol mixes. Do you know what amount of ethanol was in your fuel? Did you use anything to secure the brass inlet to the tubing end or did you simply leave it as slip-fit? It sounds like you connected your tubes to the main fuel intake since you said you have a hard time starting after draining the carb assuming you're starting with the petcock in the "on" position not "reserve".
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Old 11-16-2012, 04:16 PM   #7
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can you thread a hole at the lowest point of the tank? if so i would thread in a fitting and plumb in a on-off fuel valve so when you use all the fuel you can, flip the valve for the rest of the fuel. i did this on my steel tanks but im not sure on plastic.
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Old 11-16-2012, 05:28 PM   #8
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I've thought about that quite a bit...
I'm apprehensive about modifying my tank with no guarantee that I could get a proper seal on whatever secondary valve I'd install. Also, the lowest part of the tank is also the most forward part and as such any valve mounted there would be pretty vulnerable to debris kicked up by the front tire...I'd be afraid a good direct hit to the valve would compromise the seal.
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Old 11-16-2012, 05:54 PM   #9
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My understanding (feel free to correct me)...
My KLR has a gravity-fed carb so obviously gravity is needed to get fuel to the carb during start-up...but isn't some amount of suction created soon after start-up because the fuel flowing through the petcock down the fuel line to the carb (acted upon by gravity) creates a siphon for fuel behind it?

This is basically what I'm wondering:
Can my gravity-fed carb create the suction necessary to pull fuel through hose/tubing that is angled only slightly upwards? I have a translucent IMS tank so I would switch to "reserve" before I needed to so that the siphon/suction wouldn't be interrupted as I switched from the main petcock intake ("on") to the reserve tubing intake (I imagine switching from "on" to "reserve" as fuel is running just below the main intake opening [when one normally switches to "reserve"] could interrupt the suction with air).

I believe the set-up as outlined in my OP could actually siphon fuel upwards through the reserve hose but I imagine the flow from the siphon might not provide sufficient flow and cause fuel starvation.
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Old 11-16-2012, 06:17 PM   #10
kubiak
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on my custom metal tanks i made some of them hung lower than the carb on my xr650l so i added a fuel pump. i setup the electric fuel pump off a toggle switch so when i ran out of gas above the carb i could hit the switch and use the remaining fuel below. i didnt use a regulator so i plumbed the pump to bypass the carb with a t fitting so the carb only got what it needed then the rest of the fuel went back to the main tank through another t fitting connected to the main fuel line. hope this makes some sense.
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Old 11-19-2012, 09:17 AM   #11
Ranger Ron
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Quote:
Originally Posted by Myfuture_yourdebt View Post
What kind of Tygon tubing did you use? "Tygon® F-4040-A Fuel & Oil Tubing"? It's suppose to be resistant to swelling and resistant to gasoline/alcohol mixes. Do you know what amount of ethanol was in your fuel? Did you use anything to secure the brass inlet to the tubing end or did you simply leave it as slip-fit? It sounds like you connected your tubes to the main fuel intake since you said you have a hard time starting after draining the carb assuming you're starting with the petcock in the "on" position not "reserve".
Yes, it was F-4040-A. The ethanol is ~10%. I just used slip fit, but the slip fit was very tight before the Tygon expanded.

The petcock in my Acerbis tank has 1/8" FPT that the nylon flter screws into. I took the filter out (there is another in the fuel line) and put a short barb fitting in its place. I no longer have a "reserve", but don't need one since I can see the fuel level through the tank.

Ron
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Old 11-19-2012, 09:41 AM   #12
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Quote:
Originally Posted by Myfuture_yourdebt View Post
My understanding (feel free to correct me)...
My KLR has a gravity-fed carb so obviously gravity is needed to get fuel to the carb during start-up...but isn't some amount of suction created soon after start-up because the fuel flowing through the petcock down the fuel line to the carb (acted upon by gravity) creates a siphon for fuel behind it?
There isn't any suction because the needle and seat are above the fuel level in the carb. The end of the fuel line is essentially in the air, at least whenever the needle is off the seat.

Ron
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Old 11-19-2012, 10:24 PM   #13
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I have to admit...I am not intimately familiar with the physics of the carb, hence my questions here. And I believe what you're saying, Ranger Ron...but I just can't see how there wouldn't be a siphon effect once fuel is flowing. Completely disregarding the carb for a moment...Fuel flows down through the fuel valve during normal operation via gravity; any time this sort of thing happens, a siphon effect can occur. So if I switched from the "on" to "reserve" quickly enough, there'd still be fuel flowing down through the fuel valve and creating the siphon that could draw from the hose. I could imagine I wouldn't want to start the bike from this reserve hose unless it was last shutdown from it as well.

All my thoughts aside, I'm giving it a try on the bike tomorrow. I have some faith it might work and I don't have much to lose. It worked for one guy, or so he wrote online And he ran the hose inside his tank to the right side so it had the center "hump" to pull fuel over.
Tonight I cut down the valve's main brass tube to 1" and connected and run the Tygon as I outlined above then installed the valve on the tank [this means "reserve" and "on" are now switched assuming this works]. No leaks so far. The worse that'll happen is that the new reserve won't draw any fuel but I'll still be able to draw from the new main unless the hose is somehow obstructing flow. If that's the case, I'll ditch the reserve hose soon enough and put a taller tube back on the valve to more or less return it to how it was.
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Old 11-21-2012, 04:51 AM   #14
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Quote:
Originally Posted by Myfuture_yourdebt View Post
I just can't see how there wouldn't be a siphon effect once fuel is flowing.
There will be a siphon as long as the output (carb) is lower than the fuel level AND there is fuel in the entire tube. It all works with gravity and the weight of fuel on the "down" side pulling a bit less weight if fuel into the "up" side.

If the carb is above the fuel level, there isn't a siphon -- the carb bowl is vented so there's no "suction" to pull gas up.

If there is a SMALL air bubble in the fuel line, the weight of the gas on the carb side MAY pull the air bubble through the line and start a good siphon.

If there's a slightly larger air bubble in the fuel line, some gas may be pulled under the air and you'll have a half-assed siphon.

If the air bubble is large, the weight of the gas on the carb side may fail to pull any gas up from the tank.

One easy way to remove an air bubble from your reserve tube is to use the reserve line when the tank is full. The weight of the gas above the intake will push fuel through the tube. I'd use a smaller-diameter tube instead of a larger-diameter tube. Removing an air bubble relies on having the fuel flow faster than the air can migrate upstream. Fuel flows faster in a smaller tube and the air will migrate slower in a smaller tube.

Strap on an extra gallon of gas and test your mods.

I have worked with many siphons, but not inside a gas tank.

EDIT: I have one petcock that uses the "main" intake for normal operation and opens BOTH intakes for reserve. This would be an air leak that might kill a siphon.
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Grinnin screwed with this post 11-21-2012 at 05:23 AM
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Old 11-23-2012, 10:39 AM   #15
Myfuture_yourdebt OP
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Wow, thank you man. That was the sort of info I was looking for!
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