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half-tank lean problem!!!

Old 06-21-2006, 09:41 PM
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bennyblanco
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Default half-tank lean problem!!!

i dont know too much about rc's,so what is this problem that i hear and whats the solution?
Old 06-21-2006, 10:08 PM
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Default RE: half-tank lean problem!!!

The way to cure it is put a smaller different tank in it. I do not want to cut down on my run time and since it is not a big problem with mime I am not changing any time soon if at all. The tank is bigger at the top then at the bottom and when it gets to half full it makes the engine lean out. Some say then have a big difference and some like I does not seam to make that much of a difference but I can tell it.
Old 06-21-2006, 10:59 PM
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Default RE: half-tank lean problem!!!

so what type of tank should i get??? i have this problem with my savage at half tank my temperature gets very high!!! i have a sirio.27 on it.
Old 06-21-2006, 11:35 PM
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alvinl
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Default RE: half-tank lean problem!!!

For starters, try tuning at 1/2 tank. Run the 1st half tank then tune the motor. Refill and see how it performs. My Savage LE had this issue really bad. I was seeing swings of 50 degrees and more from full to empty. That also caused it to run like total crap until my tank was 1/3 or so empty. Try tuning at 1/2 tank first and see if it works for you. Aparently most people don't have the problem as bad as I did. But, if you rule out tuning at half tank and make sure there are no air leaks, then you can buy the kit from New Era to fix your problem. It does cut down on your run time, but it all but completely fixed my problems. Here is a link to the kit I bought:

http://www.neweramodels.com/cgi-bin/...b&part_id=1704

The tank they sell in the kit is a 125cc Ofna tank that you can get at Towers for about $10. But they also included aluminum mounting hardware to mount the tank since the stock parts will not work with this tank.
Old 06-22-2006, 03:12 PM
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Default RE: half-tank lean problem!!!

check for air leaks where in the fuel line!!! sorry if im asking stupid questions but am a newbie in the rc world!!!
Old 06-22-2006, 03:14 PM
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Default RE: half-tank lean problem!!!

ORIGINAL: savage.27

check for air leaks were in the fuel line!!! sorry if im asking stupid questions but am a newbie in the rc world!!!
Any of the fuel lines, the pressure line, fuel filter, leaks around the carb, leaks around the backplate on the motor, seal on fuel tank, etc... Fuel line is only a couple dollars to replace all of it, so it's almost cheaper to just replace it than mess with it.
Old 06-22-2006, 04:07 PM
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Default RE: half-tank lean problem!!!

thanks dude for the info!!!

Old 06-23-2006, 06:19 AM
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Default RE: half-tank lean problem!!!

Half tank lean problem doesn't exist. It's an urban legend. Tune your engine.
Old 09-21-2006, 06:33 PM
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rheeder218
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Default RE: half-tank lean problem!!!


ORIGINAL: RCaeroguy

Half tank lean problem doesn't exist. It's an urban legend. Tune your engine.
Half tank lean does exsit, i jsut experienced it with my .25 savage and it is night and day when the tank hits about half full. So does anyone have a real solution besides a smaller tank?
Old 09-21-2006, 06:42 PM
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Default RE: half-tank lean problem!!!

Here is a link [link=http://www.rcuniverse.com/forum/searchpro.asp?phrase=half+tank+lean&fuzzyMatch=on&author=&forumid=250&topicreply=combined&message=both&timeframe=%3E&timefilter=0&language=single&top=500&criteria=AND&minRank=0&sortMethod=d&submitbutton=+OK+]half tank leaning issue[/link]

Take a look at those threads and you will find that there are different ways to eliminate the half tank lean issue...
Old 09-21-2006, 07:01 PM
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Default RE: half-tank lean problem!!!

this thread is 3months old and that link doesnt work!!
Old 09-21-2006, 07:21 PM
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Default RE: half-tank lean problem!!!

Link worked for me just fine.
Old 09-21-2006, 09:00 PM
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Default RE: half-tank lean problem!!!

I do not know if someone has already gone into the fluid mechanics behind the half-tank lean problem, but the half tank lean problem does exist and is all of a result of how pressure from the exhaust pressure line is distributed on the top surface area of the fuel in the tank.

For those of you who do not know, the primary equation in this principles is:
Pressure = Force * Area.

Here is what happens: When the tank is full or near full, the top surface area of the fuel in the tank is twice that of when the tank is half empty. At a given RPM (it does not matter if it's high or low RPM), pressure form the exhaust pressure line feed constant pressure into the tank and this pressure exerts a uniform force on the top surface area of the fuel. The pressure out of the bottom of the tank is therefore relatively high.
In this case, Pressure(to fuel line) = Force(from exhaust line) * large area. See the illustration to the left below.

Now when the tank runs half way down, the top of the fuel surface area is cut in half and at the same RPM as in the above case, the pressure from the exhaust pressure line is the same as when the tank was full. The pressure at the bottom of the tank all of a sudden is cut in half too. Therefore, the velocity of the fuel going into the engine is also reduced.
In this case, Pressure(to fuel line) = Force(from exhaust line) * half the original area. See the illustration to the right below.

Anyways, a fuel tank with a uniform shape from full to empty is why many choose to switch tanks. It should not matter if the new tank in mounted on the centerline or if the tank is mounted where the old tank was (it’s just that the new tank will stick out further to the left of the Savage).

I know the pressure form the exhaust line will vary according to the RPM of the engine, but this is compensated for by the demands of the engine. For example, at idle or low RPM, the engine does not need much fuel-air and its reduced combustions push just enough pressure into the fuel tank to feed it just enough fuel. When the engine increases RPM, the exhaust pressure in the pipe increases too and trerfore pushes more pressure into the fuel tank to therefore push more fuel into the engine.
I know the pressure curve will most likely not coincide with the fuel-air consumption curve, but the engine makers had this in mind and have the right curves when they designed their engines. For example, the fuel consumption demand at higher RPM might be just a slight bit higher where as the air consumption demand would be greatly higher (thus the performance from being leaned at full trigger).

If I am missing something, please let me know.
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Old 09-22-2006, 12:12 AM
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Default RE: half-tank lean problem!!!

I bought a little 2 ounce tank that I run in line with the stock one....the little tank doesn't have a shelf so it killed the problem.....things have been alot better since
Old 09-22-2006, 08:01 AM
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Default RE: half-tank lean problem!!!

What "shelf" are you talking about?
Old 09-22-2006, 10:58 AM
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Default RE: half-tank lean problem!!!

ORIGINAL: savage.27

this thread is 3months old and that link doesnt work!!
So are you saying I shouldn't have replied to rheeder218 because he brought up your 3 month old thread?

Now I know this is going to be a shock to you (noob), but rheeder218 used a feature on this forum called a "search button" to find this old thread.. So instead of starting yet another "half-tank lean" thread.. he just simply added onto this one.. BRILLANT!!!!
Old 09-22-2006, 12:11 PM
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Default RE: half-tank lean problem!!!


ORIGINAL: SAVAGEJIM

If I am missing something, please let me know.
What you're missing is that all R/C fuel tanks do basically the same thing, slightly rich when full, slightly lean when empty. The problem comes when people tune their engine too lean, then it gets really lean toward the end of the tank and the engine rapidly overheats. The solution is to run a little on the rich side. Richen it up so that it runs good at 1/2 tank. When tuned properly you can run all day long without overheating.


(Real cars get around this problem by using a fuel pump and a pressure regulator)
Old 09-22-2006, 12:21 PM
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Default RE: half-tank lean problem!!!

Thats why some people have this problem and some dont or at least it's not so bothersome to others, its all in your tune.
Old 09-22-2006, 06:29 PM
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Default RE: half-tank lean problem!!!

i didnt see his post jack-!!!
Old 09-22-2006, 07:54 PM
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Default RE: half-tank lean problem!!!


ORIGINAL: savage.27

i didnt see his post jack-!!!
Not my problem

So next time.... try reading before you call someone out


Old 09-22-2006, 08:09 PM
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Default RE: half-tank lean problem!!!


ORIGINAL: HPI Staff


ORIGINAL: SAVAGEJIM

If I am missing something, please let me know.
What you're missing is that all R/C fuel tanks do basically the same thing, slightly rich when full, slightly lean when empty. The problem comes when people tune their engine too lean, then it gets really lean toward the end of the tank and the engine rapidly overheats. The solution is to run a little on the rich side. Richen it up so that it runs good at 1/2 tank. When tuned properly you can run all day long without overheating.


(Real cars get around this problem by using a fuel pump and a pressure regulator)
Thanks for the info.

I originally considered that the increased empty volume from the fuel being used up would cause a pressure drop, but I was under the assumption that the volume change would be too small to affect the pressure out of the tank and going into the engine. I guess that is what I get for assuming. I did'nt do any formal calculations since I do not know the dimenstions of the inside of a Savage tank, but I guess if I did, I would have discovered that this factor would have been significant and contribute to leaning.
Old 09-22-2006, 08:46 PM
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Default RE: half-tank lean problem!!!

whatever!!
ORIGINAL: fantomas


ORIGINAL: savage.27

i didnt see his post jack-!!!
Not my problem

So next time.... try reading before you call someone out


Old 09-22-2006, 09:51 PM
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Default RE: half-tank lean problem!!!


ORIGINAL: savage.27

whatever!!
ORIGINAL: fantomas


ORIGINAL: savage.27

i didnt see his post jack-!!!
Not my problem

So next time.... try reading before you call someone out



your welcome
Old 09-22-2006, 10:31 PM
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Default RE: half-tank lean problem!!!

thx!!!
Old 09-22-2006, 10:40 PM
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Default RE: half-tank lean problem!!!

My header tank solution....



2oz Hayes header tank. With the weighted pickup (clunk) in there the truck will run for a long time upside down.

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