sdh1391

thanks that is really helpfull.

twomanytoys

No problem. You may have to retune do to the increased pressure. I and most others have found that it will run very rich from the start when doing this which is a good thing and that means its working. Your tune will be more consistant now.

zztommis

OK, I'm a dork!! I can even see the end of the wire tie sticking out of the "pull thingy"!! I'm definitely gonna try this, and hopefully put the stock tank back on for the added capacity (I have the Ofna tank).
I guess figuring this out kinda gives you your 15 minutes of fame as a Savage rock star!! [sm=punching.gif]

twomanytoys

Give it a try. You will like it.

sb13

My Feedback: (52)

I know I commented that when my Savage arrives I would make this mod but I'm getting the XL and it will be here today. Maybe I missed it but does the XL need this mod or does it seem fine without it?

twomanytoys

As far as I can tell no one has complained about the mid tank lean on the XL. Even though it has teh same tank setup im sure the 5.9 puts out some massive pressure to feed the tank the whole way through. I think BUDBUD would be the one to ask about this because he has several XL's and runs the crap out of them. I have not seen him complain about anything on the XL.

sb13

My Feedback: (52)

Thanks for the reply. I'll leave it as is for now. It's charging as we speak and then off to break it in.

one-syk

i havent had any half tank lean issue's with my x 4.6

sb13

My Feedback: (52)

I'm about ready to fo outside and run the first tank through it. I went ahead and switched it over to my DX3R already, it's dailed in and ready to run now. I'll post results later.

nitro-rob

SB - how did it go?

I just broke my 4.6 engine in and am proud and embarrassed. Proud I identified the half tank lean problem independently but embarrassed I didn't notice this was a huge problem with these trucks and see this discussed all over the web before.

This topic is discussed everywhere with several opinions but little true consensus on what the cause is and what solves it.

So I have minimized the length of my lines (a recently purchased 25 I have upgraded) and put an X tank on it and will be in touch with the results after my next drive some time this week.

This seems like an interesting problem for a chemical engineer to throw some fluid dynamics equations/simulations at.

Wardster

At the end of the month I'll order a Perry VP30 Pump Regulator to keep the mixture consistent and possibly a New Era Models HSV 510 tank as well for its attitude-independence. I use to be into r/c aircaft a few decades ago and, after using a K&B40 that never ran right, I found-out Hanno Pretner ran a SuperTigre S-45abc so I bought one and added a Robart fuel pump & regulator; ended-up with a very-reliable performer no matter the attitude. I just got back into r/c with purchasing a Savage XL a month ago or so; for which I have on order, right now from the lhs, the exponential-capable 3-channel Spektrum dx 3.0 package, w/two receivers & digital servos, and a Spektrum Nitro Telemetry Combo Pack [SPM1300] to monitor receiver voltage and head temp, to help with monitoring fuel mixture.

Anyway, to make a long-story short, lol, I guess that's the fuel tank solution I'm going to go with.

quietnas1

I know this is an old thread but I'm going to give this a try. I noticed when my hits half tank it feels like it wants to shut off between shifts. When I fill her back up it runs fine. I didn't tune from half tank I tuned from a full tank. This mod seems to be a sure shot.

nitro-rob

You likely have half lean. I just installed a mid tank and can't test it because of the weather.
My truck is horrible for half tank lean. At the end of the season I went out on a cool day and obviously had to run a lot richer and there was no half tank leaning which makes me think that it doesn't happen as badly when the the hs needle is open a lot.

quietnas1

Well I shortened both lines. I shortened the exhaust line by 3 inches and shortened the fuel line by about 6 inches and it worked great.

Edit: I thought I would elaborate a little more. My shifts are nice a and crisp now all the way to almost an empty tank. It seems to be way more responsive and only started leaning again when there was really no visible fuel left in the tank. I flipped it on its lid about 5 times and it only shut off once. I think this free no cost out of your pocket mod works great.

carfanatic

i"m going to run my fuel lines like this on my 4.6 see what happens... I just hope I have enough room for the fuel filter!

kurtf5

So what is the scientific explanation as to why a shorter fuel line makes a difference?

Argess

That's the rub. It's hard to promote a fix when the theory is lacking.

On the surface, the fuel line is not the same as the pressure line with respect to restrictions. Fuel flow is slow, so not an issue. Gravity...well, the fuel line starts and ends in the same places, regardless of it's length.

My best guess is some sort of flow issue due to ....hmmm.....what's the right word? Like the surface tension on water. So even though the fuel is moving slowly, it still resists movement due to this "adhesion" quality and so a shorter line helps.

Best I can do.....LOL.

quietnas1

Bottom line is if it doesn't work out for you, you have nothing to lose but a few inches of fuel line. It worked great for me! Thats all I can say. The hell with theory my truck runs alot better.

Argess

Nope......never say "the hell with theory".....bad thinking!!! It is difficult to fix something when you dont' understand why it works. May not obviously apply to this little fuel-line thing, but understanding is the key to success.

quietnas1

Agreed. But with the fuel line thing since you really have nothing to lose I cant see why some one would not try it.

Argess

Yes, you're right...I think we agree, and certainly, shortening all lines is worth a shot.

I did in fact try it (shortening the fuel line), but not on my Savage. I tried it on an OFNA 1/8th buggy. It did seem to cure the 1/2 tank lean, but it never was much of a problem on the buggy as I had already shortened the pressure line. But it did seem to eliminate any little bit of the symptoms still there.

I think the header tank and then the mid-tank mods were the first to adress the 1/2 tank lean issue. They are the most labour intensive mods to implement. But everyone still seems to want to do them. Twomany toys has the cheapest method......shorten ALL lines. Then there's the "reduce the exhaust outlet diameter to increase the pipe pressure", which is the next cheapest and easiest. After that, the next cheapest and easy mod is my modified uniflow with one-way valve mod. All easy. All will help reduce or eliminate the problem. But still.....most people still go with the new tank and re-location effort.

If they'd take the time to try to understand what's going on, they'd probably pick one of the cheaper, easier methods. That's what I was getting at. And as I said, I think we agree.

nitro-rob

I think most people just put up with it and keep the tank full. Those mods didn't work for my savage. I always run minimal length lines to minimize pressure drop.

I wonder if another fix would be to put the pressure outlet on the exhaust closer to the engine. Exhaust pressure drops across the pipe so there would be more pressure. Its just an idea and all theory.

nitro-rob

Some thoughts on the theory. I work and am trained in this area and have put a lot of thought to this although I havn't searched for any relevant literature or anything but I have talked to my chemical engineer colleagues about it.

If the carburetor isn't getting enough fuel and the fuel is supplied by pressure by the fuel line there must be a loss of pressure. Pressure across tubing, whether it is flowing liquid or air, drops as it travels across the line. This effect increases as the diameter of the line is decreased. Hence shortening lines will help reduce the problem.

The question then is why does the pressure change going from the top to the bottom of the tank? Tank geometry changes on the bottom half, the weight of fuel decreases, the void volume increases as the tank drains and the carburetor inlet is located around the middle of the tank. This makes me think that the stock savage setup provides just enough pressure to work well when the tank is full and gravity etc.. and it doesn't take much to reach the tipping point where the pressure isn't sufficient causing leaning. I suspect that when I am running my savage very rich the large needle opening allows things to flow more and isn't as sensitive to pressure fluctuations.

What I can't get a handle on is how variation in tank pressure changes with RPM. Obviously pressure increases as RPM goes up but what is the relative difference in pressure from low to high RPM the same at half tank and full tank.

This is all speculative with some scientific reasoning behind it. I said it over a year ago - fluid dynamics simulations would solve this problem.

kurtf5

Well ive cut my lines now but i cant test it till the weather gets better. Its cold here anyway though so i doubt half tank lean will be a problem.
My exhaust line was very long, it went around the long way past the backplate and round to the exhaust. God knows why it was built that way, would cut costs just to sell the Savage with shorter lines anyway.

jbooker82

My Feedback: (4)

I just tune my savage at half a tank with the short lines. A little doggy but will still wheelie at full tank, 3/4 to 1/4 runs strong, 1/4 to empty, mad wheelies.