Half tank=lean!!!
07-26-2004, 05:52 PM
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Half tank=lean!!!
hi, this is a problem with the savvys,i settle my needles with full tank but when it goes half the truck goes way too lean[X(] is there any way to solve this?
i think that i read some about a longer fuel tube that goes from the exaust
why this happens?
help here...
i think that i read some about a longer fuel tube that goes from the exaust
why this happens?
help here...
07-26-2004, 06:23 PM
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RE: Half tank=lean!!!
no no no no, don't do the dual tank mod. here is something that is $10, takes 5 min to install and works a lot better!
http://www.savage-central.com/ftopic22106.html
this will work very, hope it helps.
http://www.savage-central.com/ftopic22106.html
this will work very, hope it helps.
07-26-2004, 11:12 PM
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RE: Half tank=lean!!!
how is this setup better than the dual tank mod? with the dual tank mod u can run up side down. Also, I don't particularly see how this setup would provide superior performance over the dual tank mod when your the right way up. Part of the lean condition is caused by fuel sloshing around, causing a lean issue when the fuel moves away from the fuel pickup, how does this prevent this or stop it from being a problem???
07-26-2004, 11:28 PM
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RE: Half tank=lean!!!
hmmm.. just finished reading the entire thread. sounds like it does work but it does have its problems. I think I'll just stick with my dual tank mod, I've had no problems with it and even with the header tank empty u only have to fill it part way up before the tank fills itself while running.
07-27-2004, 06:13 PM
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RE: Half tank=lean!!!
i saw that the stock tank have kind of hole/tip already down the cap,so is really necessary to drill and put the metal pressure fitting in it?
maybe a larger fuel tube will just enter the tip down the cap
what do you guys think?
maybe a larger fuel tube will just enter the tip down the cap
what do you guys think?
07-28-2004, 12:39 PM
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RE: Half tank=lean!!!
There are tons of options for the UNIFLOW.
It works AWESOME! It costs you NOTHING to try.
I've tapped the tank lid with a pressure fitting, run some tubing and am using a clunk.
But others have stuck an antenna tube in there and nothing else!
It works fine also with pressure fitting and fuel tubing only. A $1.50 fix. Give it a try.
Just make sure you put the end of the tube in the baffle where the fuel pick-up is.
Marco.
It works AWESOME! It costs you NOTHING to try.
I've tapped the tank lid with a pressure fitting, run some tubing and am using a clunk.
But others have stuck an antenna tube in there and nothing else!
It works fine also with pressure fitting and fuel tubing only. A $1.50 fix. Give it a try.
Just make sure you put the end of the tube in the baffle where the fuel pick-up is.
Marco.
07-29-2004, 12:30 AM
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RE: Half tank=lean!!!
Yup...
BTW, I was the guy who first did the mod... that's why my avatar is the same. You can try it for the cheap by cutting some antenna tubing and stuffing it in the lid, just lengthen the silicon tubing (to around 12 to 15") from the muffler to the tank to prevent overspill.
For the .21 tanks, you might also try reversing the carb/pressure feeds, meaning the line from the lid will go to the carb and the standard front fuel vent will be used for the pressure line.
I'm so glad word of the mod has spread to other forums as well.
BTW, I was the guy who first did the mod... that's why my avatar is the same. You can try it for the cheap by cutting some antenna tubing and stuffing it in the lid, just lengthen the silicon tubing (to around 12 to 15") from the muffler to the tank to prevent overspill.
For the .21 tanks, you might also try reversing the carb/pressure feeds, meaning the line from the lid will go to the carb and the standard front fuel vent will be used for the pressure line.
I'm so glad word of the mod has spread to other forums as well.
07-29-2004, 09:36 AM
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RE: Half tank=lean!!!
jwan...
I wish I could... but like I said in the original thread in savage-central where I first experimented with it, I DIDN'T invent uniflow. It's a trick we use in the r/c aircraft community both to improve engine performance and prevent a flame-out which is something aircraft flyers dread.
If you're more interested to find out more, try this link;
http://www.fraserker.com/heli/uniflo...flow_works.htm
I wish I could... but like I said in the original thread in savage-central where I first experimented with it, I DIDN'T invent uniflow. It's a trick we use in the r/c aircraft community both to improve engine performance and prevent a flame-out which is something aircraft flyers dread.
If you're more interested to find out more, try this link;
http://www.fraserker.com/heli/uniflo...flow_works.htm
07-29-2004, 09:56 AM
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RE: Half tank=lean!!!
I'm curious... that explanation involved the use of a fuel line with a clunk at the pick up as well, ensuring that pickup is always submerged in fuel to a degree, but since our tanks don't have a clunk at the pickup, in the old 21 tank (and for the new 25 tank when accelerating backwards) wouldn't you still experience a large pressure difference as fuel is actively being pushed away from the pickup? with a header tank, where the volume is smaller, and where a clunk can also be used, the effect of this is reduced.
maybe I should try doing both mods and see what happens... but first I need to save enough money to buy fuel... I'm broke =(
maybe I should try doing both mods and see what happens... but first I need to save enough money to buy fuel... I'm broke =(
07-30-2004, 07:40 AM
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RE: Half tank=lean!!!
There are 2 factors contributing to pressure in the tank.
The first is the pressure hose from the exhaust the second is gravity.
Where the pressure from the exhaust enters the tank has no effect on total pressure so whether it enters at the lid or into the fuel makes no difference on fuel pressure. It could though introduce bubbles in the fuel i guess. The effect of gravity is simply a matter of how much fuel you have in the tank. Putting the fuel in a second tank higher up increases pressure in the carb (a higher hydrostatic pressure), pumping fuel from the original tank to the extra tank and keeping this second tank at an equal level untill the original tank is empty will give a more even pressure at the carb eliminating differences in pressure and in that way eliminating leaning problem. (If the extra tank is completely full it will have no effect on the pressure at the carb end as it then would be equal to a siphon and only the level of the ends matter.)
Why the uniflow eliminates leaning problems in this case is not obvious to me, but what is is that pressure distributes evenly and is a matter of forces acting upon the fuel.
Backing or turning so fuel sloshes around does not affect pressure but gravity forces on the fuel actually in the fuel lines does. Thats why a truck with the tank on the left side tends to lean in right hans turns.
One way valves both on pressure and fuel lines should do more good. Fuel sloshing into the pressure line on a full tank will affect pressure.
The first is the pressure hose from the exhaust the second is gravity.
Where the pressure from the exhaust enters the tank has no effect on total pressure so whether it enters at the lid or into the fuel makes no difference on fuel pressure. It could though introduce bubbles in the fuel i guess. The effect of gravity is simply a matter of how much fuel you have in the tank. Putting the fuel in a second tank higher up increases pressure in the carb (a higher hydrostatic pressure), pumping fuel from the original tank to the extra tank and keeping this second tank at an equal level untill the original tank is empty will give a more even pressure at the carb eliminating differences in pressure and in that way eliminating leaning problem. (If the extra tank is completely full it will have no effect on the pressure at the carb end as it then would be equal to a siphon and only the level of the ends matter.)
Why the uniflow eliminates leaning problems in this case is not obvious to me, but what is is that pressure distributes evenly and is a matter of forces acting upon the fuel.
Backing or turning so fuel sloshes around does not affect pressure but gravity forces on the fuel actually in the fuel lines does. Thats why a truck with the tank on the left side tends to lean in right hans turns.
One way valves both on pressure and fuel lines should do more good. Fuel sloshing into the pressure line on a full tank will affect pressure.
07-30-2004, 07:48 AM
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RE: Half tank=lean!!!
ORIGINAL: Norrmannen
There are 2 factors contributing to pressure in the tank.
The first is the pressure hose from the exhaust the second is gravity.
Where the pressure from the exhaust enters the tank has no effect on total pressure so whether it enters at the lid or into the fuel makes no difference on fuel pressure. It could though introduce bubbles in the fuel i guess. The effect of gravity is simply a matter of how much fuel you have in the tank. Putting the fuel in a second tank higher up increases pressure in the carb (a higher hydrostatic pressure), pumping fuel from the original tank to the extra tank and keeping this second tank at an equal level untill the original tank is empty will give a more even pressure at the carb eliminating differences in pressure and in that way eliminating leaning problem. (If the extra tank is completely full it will have no effect on the pressure at the carb end as it then would be equal to a siphon and only the level of the ends matter.)
Why the uniflow eliminates leaning problems in this case is not obvious to me, but what is is that pressure distributes evenly and is a matter of forces acting upon the fuel.
Backing or turning so fuel sloshes around does not affect pressure but gravity forces on the fuel actually in the fuel lines does. Thats why a truck with the tank on the left side tends to lean in right hans turns.
One way valves both on pressure and fuel lines should do more good. Fuel sloshing into the pressure line on a full tank will affect pressure.
There are 2 factors contributing to pressure in the tank.
The first is the pressure hose from the exhaust the second is gravity.
Where the pressure from the exhaust enters the tank has no effect on total pressure so whether it enters at the lid or into the fuel makes no difference on fuel pressure. It could though introduce bubbles in the fuel i guess. The effect of gravity is simply a matter of how much fuel you have in the tank. Putting the fuel in a second tank higher up increases pressure in the carb (a higher hydrostatic pressure), pumping fuel from the original tank to the extra tank and keeping this second tank at an equal level untill the original tank is empty will give a more even pressure at the carb eliminating differences in pressure and in that way eliminating leaning problem. (If the extra tank is completely full it will have no effect on the pressure at the carb end as it then would be equal to a siphon and only the level of the ends matter.)
Why the uniflow eliminates leaning problems in this case is not obvious to me, but what is is that pressure distributes evenly and is a matter of forces acting upon the fuel.
Backing or turning so fuel sloshes around does not affect pressure but gravity forces on the fuel actually in the fuel lines does. Thats why a truck with the tank on the left side tends to lean in right hans turns.
One way valves both on pressure and fuel lines should do more good. Fuel sloshing into the pressure line on a full tank will affect pressure.
i really dont understand this one physics thing[
]but if a lot of ppl say that works...
07-30-2004, 08:03 AM
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RE: Half tank=lean!!!
No I'm just saying the tube that moves the pressure inlet from the cap to below the fuel surface does not really explain why it works, as it will not change the total pressure. This is probably quite unnecessary to do. Actually it should rather create than solve problems as you'll more easily get fuel into the pressure line.
Fuel in the pressure line is affected by g-forces much more than only air, thus creating larger pressure differences.
The longer pressure line may have effect creating a bigger reservoir of pressurized air.
Actually I think you'll have to look at the problem as rather a rich when full rather than leaning when empty to solve the problem. You would want to have a higher gas pressure as the tank is emptying to compensate for the decreasing pressure caused by gravity.
Fuel in the pressure line is affected by g-forces much more than only air, thus creating larger pressure differences.
The longer pressure line may have effect creating a bigger reservoir of pressurized air.
Actually I think you'll have to look at the problem as rather a rich when full rather than leaning when empty to solve the problem. You would want to have a higher gas pressure as the tank is emptying to compensate for the decreasing pressure caused by gravity.
07-30-2004, 09:01 AM
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RE: Half tank=lean!!!
The point of this mod is not to increase pressure in the tank. It just stops the pressure from escaping through the pressure line. In a tank without this mod the pressure can easily escape through the pressure line of the pressure in the tank is greater than the pressure comming in. In a tank with the mod since the pressure line is basicly submerged the fuel acts as a one way valve to keep the pressure in the tank.
07-30-2004, 09:15 AM
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RE: Half tank=lean!!!
Yeah that'll work untill the pressure diff is big enough for the fuel to siphon out....
Why not just put in a one way valve just ahead of the tank. It's at around $ 5 and requires only a pair of scissors to cut the tube, then slide the tube on the valve...
Would actually be good for those with this mod to have a oneway valve to avoid loosing fuel which I have read can be a problem when using this mod....
To me it's obvious that gravity is playing a rather big part here. Fuel sloshing into the pressure tube is mainly a problem when tank is too full. This won't compensate for loss of gravity pressure.
An extra tank higher up will as long as there is air in it..combine it with a one way just a head of it an you'll benefit all the way...even pressure both from exhaust pressure and gravity.
Why not just put in a one way valve just ahead of the tank. It's at around $ 5 and requires only a pair of scissors to cut the tube, then slide the tube on the valve...
Would actually be good for those with this mod to have a oneway valve to avoid loosing fuel which I have read can be a problem when using this mod....
To me it's obvious that gravity is playing a rather big part here. Fuel sloshing into the pressure tube is mainly a problem when tank is too full. This won't compensate for loss of gravity pressure.
An extra tank higher up will as long as there is air in it..combine it with a one way just a head of it an you'll benefit all the way...even pressure both from exhaust pressure and gravity.
07-30-2004, 09:50 AM
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RE: Half tank=lean!!!
That's the reason for the extra long pressure line. With a longer retrun line the pressure in the tank will be enough to keep fuel fowing to the carb but not enough the cause the fuel to be pushed out the pressure line.
07-30-2004, 10:07 AM
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RE: Half tank=lean!!!
I use a longer fuel line to avoid sloshing problems with a very full tank, it helps somewhat. In theory it's correct that this set up will even out the pressure differences as the gravity forces working on the fuel backing up the pressure line will resist the backpressure better than only air/exhaust. But then we're back to what I pointed out earlier on. Why invest $ 10 in this system that requires some modification of the tank when you can do the exact same thing with a one-way valve at half the cost and no mods but cutting the presssure or even better the fuel line, hell do both to be sure...
07-30-2004, 10:29 AM
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RE: Half tank=lean!!!
You are correct that one way valve will accomplish the same thing. The only thing is that I have heard of people having problems with that setup forcing fuel into the carb after a high speed run. The reason being is that the one way valve set up does not have a pressure release mechnism if the pressure gets too high. With the tank mod set up the pressure will temporarly push the fuel part of the way up into the tube until the high pressure is relieved.
08-02-2004, 06:27 AM
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RE: Half tank=lean!!!
ORIGINAL: jwan
people have tried using one way valves before, it apparently caused lean problems
people have tried using one way valves before, it apparently caused lean problems
I tried a one-way buld/primer being used solely as a one-way valve (from an mgt I think) and when going from heavy throttle to light/no throttle it floods the motor. Also on starting it can flood the motor like nobody's business.....
