Argess

I posted this in another forum and it seemed to generate interest, so I thought I'd re-post it here.

OMG, you are all saying, but I did figure out a mod that worked for me, and thought I’d share it with you.

First of all, I addressed this issue a while back when I was thinking of the dynamics of “how fast the tank can pressurize” with respect to a full tank vs. an almost empty one. My final thought on this was to decrease the pressure line restriction, and this mean shortening the pressure line as much as possible. I have tried this in 1/8 Buggies and it works great. It also reduced the problem in my Savage 25 to an acceptable level, but you can only make it “so short”.

Second of all, is the actual “head pressure” change as the fuel level drops….a more ”static” evaluation, as the level doesn’t drop quickly during engine operation. Although muffler pressure reduces the percentage change that the HSN/Carb “sees”, there still can be an issue with this dependant on the engine you use. (I really didn’t have much of a problem with the Nitro-Star 25 after I shortened the pressure line.)

Anyway, apparently some engines seem to react differently to this Savage fuel tank issue, and with our newly installed OS 30VG, the ½ tank, lean problem became more noticeable.

I was reading with some interest on the Uniflow system, but it had drawbacks. The worst one was fuel coming back and draining out the muffler, or with a 1-way check valve in the pressure line, the engine flooding when stopped for some reason. So I decided to try to improve it.

Please forgive my bad sketch, but referring to it, here goes:

Engine at a fixed or accelerating RPM:

1) Good exhaust pressure at “A” and “B” and “D”
2) Reduced pressure by fuel “head” at “C”
3) One-way Valve closed as pressure at “A” is greater than at “C”

Engine deceleration:

1) Pressure is reduced at “A”
2) One-Way Valve is open as pressure at “A” is now less than “C”
3) Exhaust gas flows more quickly from “C” to “A” (than fuel from “B” to “A”) so tank pressure is reduced before any of the pressure line fills with fuel.

So I tried it tonight. Absolutely no variation in performance or temperature from a full tank to an empty one. No fuel coming out exhaust. No flooding of engine. Success!!!

Also attached is a picture of the installation. Not very “clean” as I wasn’t sure it would work.

I really didn’t want to start any sort of argument about one mod being better or worse than another, but I am hoping that someone else will try this and let me know how they made out.

You need:

1) some extra fuel tubing
2) a barbed, thread in fuel fitting
3) a one-way valve
4) a T-Connector




Nipple was a 8-32. I drilled a hole smaller than you would if tapping metal and only partially tapped the hole (tapered tap not all the way through). Nipple started getting snug long before gasket was compressed. Very tight. Same concept as a nylon loc-nut.

This may not be the best place for the nipple, as it and the pressure line are kind of exposed. Below is a pic of an alternate arrangement that would do the same thing. Basically a nipple (say a 10-32 for 1/8 hose) drilled out to accept a brass fuel tube, and the two soldered together. Tube length cut so end is about 1/8" from bottom of tank.



There is one draw-back to this mod. You get no warning when you are about to run out of fuel, so it's possible that you might be making a screaming long distance pass when it runs out. I sort of liked the warning signs of it getting lean so I could be taking it easy when it ran out of fuel.

An up-side, is that the engine warms up very fast as it isn't running with a rich mixture for the first part of the tank. This helps reduce wear.

Here's the P/Ns I used:

T-fitting: Robart 221 http://www3.towerhobbies.com/cgi-bin...?&I=LXES20&P=7

Nipple: Du-Bro 539 http://www3.towerhobbies.com/cgi-bin...&I=LXD623&P=ML

One-Way Valve: Yamada YS0405 this was an expensive unit, but all the LHS had. I suggest this instead: Fourmost 138 http://www3.towerhobbies.com/cgi-bin...&I=LXG850&P=ML

rcnitrohead

I saw this while in school today (whoops[sm=red_smile.gif]) and it looks pretty interesting. I was thinking about using a Mugen tank, but if this works then I may opt for it. Good find!

Wisconsin Nitro

would be allot easer to do then the other one mod were you have to fab a bunch of stuff

IBrakeForNobody

My Feedback: (16)

Sounds very interesting. I just called up the LHS and ordered the parts to try this out. I currently have my own version of the New Era Ofna tank mod, but the 125cc capacity is kind of hindering. I'll let you know how it goes.

So to simplify what you wrote, the second pressure line in the fuel itself is to make up for the lost exhaust pressure during negative acceleration (as my old physics teacher could tell you, "There is no such thing as 'deceleration'" ) Is that remotely close to what you meant? [sm=confused.gif]

I just thought of something...if there is a pressure line in the fuel itself, wouldn't that cause the fuel to bubble, therefore lowering the density of the fuel, therefore leading to more air bubbles in the fuel line from the tank to the carb?

Argess

Introducing a presure line at the same level in the fuel as the pick-up ensures the pressure remains consistent at the pick-up for a given engine rpm (muffler pressure) regardless of the fuel level in the tank. This is what the Uniflow mod does.

I have added the one-way valve (and line), so that when the engine rpms drop (and muffler pressure drops), the air/exhaust in the tank can immediately escape and thereby prevent the contained pressure from either pushing fuel back out the pressure line to the muffler, or flooding the carb (resulting in a bog when you again accelerate), or both.

The bubbles merely rise to the top of the tank, and are not picked up by the tank pick-up to the carb.

ps:and yes,.....negative acceleration vs deceleration.......chuckle.

pps: I'm quite excited about this mod as it is cheap and easy to do. Other mods are fine, so I'm not saying this is better. But it seems to work great so far.

twomanytoys

Do your temps pretty much stay the same throughout the whole tank with this mod? Also why have teh one way valve to prevent fuel from backing up into the line when there is no pickup in the tank on the cap. How would fuel get up there? I can see it with the uni flow mod but not with this one.

Argess

Yes, they did. To make the test reasonable, I kept the same driving style throughout the test as obviously the engine will get hotter on 100 yard WOT runs through grass. So I kept doing the same WOT runs, the same wheelie action, the same stops and starts, one after the other and then kept repeating the routine until the tank was gone. I must have measured the temp at least 10 times during the run....each time, immediately after coming in after the high speed run part of the routine and checking directly at the glow-plug.

Basically, the engine will run as it did when the fuel level was low with the stock set-up. If you were having a very lean end to your run, you may have to richen things up a bit. I had mine tuned just about perfect for near the end of a tank, so it was very rich at the beginning with the stock set-up. After I did the mod, it was fine throughout the tank without any new tuning.

Once the engine got to temp, it stayed there for the whole rest of the tank. Naturally performance gets better once the engine warms up. Knowing that, I should have immediately run another tank while the engine was still warm. That's for another day.

Edit....the 1-way valve lets the gas (air/exhaust) pressure out of the tank when you let off the throttle. This way the tank doesn't stay pressurized and load up the engine with fuel at an idle, and/or drive fuel back up the other pressure line into the tuned pipe.

rcnitrohead

Ibrakefornobody: When you get the parts in try it out, make sure to update this thread. I just took my STS .30 for a spin and the temps vary a crazy amount throughout the tank. Half-tank lean is extremely noticeable, and if this works I'll do it pronto Tom.

Argess

Quick Update: I went to the LHS to order some of those cheaper one-way valves so I could mod some of my other vehicles, plus have a spare one kicking around. The HS guy told me that the reason he stocks the Yamada, is that its the one they've had the best luck with (in other, but unknown applications). So, here's link that shows the check valve I used (which I know works fine):

http://www.ronlund.com/Merchant2/mer...ct_Code=YS0405

I'll try the other type (Fourmost) once they arrive, and if there's any problem with them, I'll post it here.

losacco

I tried this mod today, seems to work great. No lean issues and constant temps all day. I used the one way valve from Tower, seems to be working fine.

IBrakeForNobody

My Feedback: (16)

I got the parts in a few days ago...now I just gotta find some time to do a baseline test then mod the tank and test it again. I hope to mod the tank in the next week or so...I'll update when I finish.

Argess

Ahhh.....finally....someone else tried it and had success. Yes!!!! Thanks for posting that Losacco.

Well.....there is one negative thing about this mod. After a lot of use, the one-way valve gets a little sticky......needs to be flushed with alcohol once in a while. Didn't seem to affect operation of the truck, but I noticed it took a gentle puff of air to open it, and when it was new, it seemed totally open in the one-direction. Not sure if Nitro-Cleaner would have an affect on the silicon flapper valve inside or not....... For me, cleaning it once in a while is acceptable.

go-to

My Feedback: (2)

Great variation of the Uni-flow mod. That mod simply extends the pressure line from the tank cap with fuel tube inside the tank down to the bottom of the tank.

[)]

dhyde79

my only problem with this, is the potential for feeding fuel to the muffler once the truck's upside down (as mine tends to be on occasion)

Argess

Yes, I know what you mean, but the mod makes that situation no worse than the stock set-up.

Mine has landed upside down many times since I did the mod, and I havn't noticed any fuel coming out the pipe.

What I have noticed, is a significant increase of run time as the engine isn't wasting fuel during the early part of the tank, when it used to be rich before the mod

Parputt537

Hmmmmmmmmm, me likes[sm=thumbup.gif]

rcnitrohead

I'll order the parts this weekend hopefully I appreciate you bringing this mod to our attention. I'm surprised it's getting so little feedback. 100's of people here (including me) have complained about the half tank lean. This is a mod that takes 20< minutes and costs under $20, so it seems good to me[8D] Thanks, Argess. Tom.

go-to

My Feedback: (2)

I have the parts ordered as well. We shall see.

I'm putting this on my S-25 with the ported Surefire 32R which is very cold-natured. Of course it's only about 10 tanks into break-in and that is a big part of it.

go-to

My Feedback: (2)

Here's mine. Haven't run it yet though.

Argess

I just picked up a couple of the less expensive Fourmost plastic check valves a few hours ago. I can't recommend them. In fact, I dont' think they will work well at all, although someone did post they got good results earlier in this thread. Anyway, they exhibit far too much "cracking pressure" (or "stiction") to open them.

The Yamada valve works fine, plus it can be easily taken apart and cleaned. A bit more expensive, but in this case, it turns out you "do" get what you pay for. Now.....what am I going to do with these two valves I don't want to use..........

BrandonFox28

Great idea, dude. I'll have to try it out.

Argess

Hello again….. So there I was last night, with two Fourmost valves I don’t know what to do with and I start feeling guilty about those of you who may have bought one and are now cursing me because you’ve drilled a hole in your fuel-tank. So I came up with a solution….how to modify your Fourmost valve.

It’s fairly easy, only takes a few minutes, and a sketch is included below and so are the instructions on how to do it. In the end, you get a valve just as good, if not better, than the Yamada valve.

1) First, take the valve apart. To do this, use a small jeweler’s flat bladed screwdriver. Not the smallest one you one, but maybe the next one up in your set. Work it around the valve where the white and red plastic housings meet. This will relieve the pressure of the white part where it turns in a bit over the red housing. Once you’ve gone around once, start going round again, but from time to time, pry gently with the screwdriver until you see the two parts start to separate. Then you can just pull it apart by pulling on the two barbed ends.

2) Next, clean the oil of the parts. I’m not sure why this oil was there…possibly to aid in automated assembly, possibly to keep the silicone-rubber flapper in good shape during long-term storage, whatever. But clean it off.

3) Now you modify the white housing. Using a sharp x-acto knife blade, insert the tip into the air-hole on the inside of the white housing and rotate it gently to make a chamfer. Do not use a drill bit, as it will gouge and ruin the housing. Make the top of the chamfer about twice the diameter of the original hole. This will allow more air-pressure against the flapper valve and in fact increase the force against the flapper valve by a factor of 4, so much less air-pressure is needed to open the valve. Additionally, since less flapper valve rubber to white housing contact is now there, less “stiction”, due to exhaust residue, will be present.

4) Now the tricky part. You must remove any flash around the edge of the chamfer. I call this “chamfering the chamfer”. A flat-bladed jeweler’s screwdriver in combination with your x-acto knife will do the job. A perfectly flat inside of the white housing is required.

5) Clean out the white housing again, and re-assemble. Note that the flapper valve has a step in it. The step goes towards the red-housing. The flapper must be fitted into the red housing first, and goes in until flush. Then snap the two housing back together.

6) Now test it. The most gently puff applied to the white end should flow freely through the valve. Now try the red end….gently at first, and then as hard as you can. At no time should there be any air-leak. If there is one, you must have missed some flash, and you need to take the valve apart again.

losacco

Where can I get the Yamada? The one post is out of stock.

Argess

My LHS has a website, but it doesn't list the valve. I think they do have stock. Best to e-mail or call. Here's the link:

http://www.rcwings.com/

losacco

Hey thanks....I found it at Horizon Hobbies.