d-slo

Sweet!

twomanytoys

Just so you know you done need all these mods and gizmos for the half tank lean condition. I found the easiest and most simple fix and it works awsome. Almost to the point to where you dont even notice the problem. Here is my post. Follow this and you will be all set. I have got sooo many great responses from this forum and others about this and wondering why no one thought of this years ago. COme to think of it I have not had anyone say it did not work. Try it and you will like it. It makes the engine run so much better, keeps a tune easier and alot easier to tune from the start.

http://www.rcuniverse.com/forum/m_75...tm.htm#7538776

Triscuit

nice, your truck looks really clean. Have you gotten a chance to run it yet?

mubus

i am planning to do this mod for my xl sometime this week
i wanna make sure i got the parts right

one way valve
http://www.greathobbies.com/producti...rod_id=YSE0405

t fitting
http://www.greathobbies.com/productinfo/?prod_id=ROB218

pressure fitting
http://www.greathobbies.com/productinfo/?prod_id=DUB539

just wondering why do you put the one way valve from between the t valve and the tank cap, instead of between the t valve and the pressure fitting?
thanks =D

Argess

Those parts look correct, except for the T-fitting. Get the 1/8th ones, Robart P/N 221. http://www.greathobbies.com/productinfo/?prod_id=ROB221

Don't run your tap all the way through the hole you drill. Just a little ways. When you install the fitting, it will self-tighten as it makes the last threads. The tank is only plastic, so don't over tighten it.

Also, take the one-way valve apart before you use it and clean the little clear flapper valve with alcohol. Pat dry with Kleenex and re-install.

The idea is to pressurize the tank at the level of the pick-up, so that pressure is the same no matter what the fuel level in the tank.

The one-way valve let's air out of the top of the tank when you let off the throttle (when muffler pressure drops). If it wasn't there, fuel would go up the other line (from the air-pressure)and get back into the muffler.

Triscuit's installation pic (oops....Go-to's pic in Triscuit's post) above looks good. Don't forget, keep that pressure line as short as possible. The fuel line can remain at it's original length with this mod.

Twomanytoy's mod of shortening ALL the lines is the cheapest, however I'm not convinved it works for all engine/muffler combinations. Plus, uspide down, the enigne will run out of fuel quickly from the short line. It may be worth a try though.

wolfie1

thats an interesting sounding mod which doesnt involve moving about tanks and radio gear, am def well interested to hear of your results i am gonna try some place here in the uk so i can try out this mod

mubus

lol well my new years rc budget comes to 158 dollars including these parts..
.. its a new year, so i will be needing new stuff =D

mubus

just a question...
fuel won't flow out though the muffler with the fuel tube inside the tank will it when you are priming and etc[&:]
and when you are tryin to attach the dubro brass nipple do you drill a hole at the top of the tank and screw the thing in?
i just want to make sure i do this right before i end up needing to buy another fuel tank:P

Argess

No problem with priming. Plug the exhaust and crank it over. That pressurizes theo tank. Say it doesn't start right away....when you take your finger off the exhaut, the built-up air pressure in the tank escapes through the one-way valve instead of fuel coming back up the other line.

No, the fitting goes in the front side of the tank, close to the bottom. Check out some of the completed installation pics in this thread. Re-read the theory post. It's probably a good idea to fully understand this mod before doing it. In fact, I won't do anybody's mod if it doesn't make sense to me.

Maybe this will help:

The fitting goew in the bottom so the pressure at that point is always the same at a given rpm, regardless of the amount of fuel in the tank. The bottom of the tank is where the pick-up is, so that's where we want the pressure to be consistent for a certain rpm.

Argess

I did have one fellow complain about the mod. He left fuel in his tank after he was done for the day. Fuel did leak forom the exhaust during the night. As hard as we try, it is virtually impossible for there not to be a tiny bit of "stiction" with a one-way valve. Once he brought his vehicle into the house, where it was slighlty warmer, the tank started to pressurize very slowly and fuel seeped back up because the valve was sticking. Simple solution.....don 't leave fuel in your tank when done for the day, plus make sure the valve is clean so it doesn't stick.

Surprisingly, valve cleaning maintenance is not a problem. I thought I'd be cleaning it all the time, but so far I've only cleaned it once, and that was because I thought I should. It's factory gook-um that is the problem, much more so than fuel residue from use. So that intial valve cleaning is important.

mubus

lol after reading your theory over and over again... i finally get it =D

Argess

A+++ Good for you! One of the reasons I never did the header tank or mid tank mod was that I wasn't really certain how thye worked, so you're not alone.

On drilling the tank hole......think how worried I was as the mod was experimental and I had no idea if it would work well or not.

eyeopenher

i would like to say i just did this mod and it seems to work well. my savage had a bad arse htl...  now it seems to have flattened out. loving it. very simple to do and works wonders... thank you for the info... 

smitty2919

lol or just unplug the line going to the top of the tank so there is no way for the tank to pressurize.

This mod looks great. I just picked up a Savage 3 weeks ago and noticed something was "up" with the tune once it got half tank to empty tank. Not knowing there was an actual name for it until I stumbled upon it in some threads.

I'll have to try this soon. Thanks for the great writeup. But along with it dumping fuel to the muffler upon flipping over, it would be no diff than the stock setup with the line from the muffler to top of the tank.

Also what about adding another check valve between the T fitting and the barb fitting at the bottom of the tank. That way you are creating two "one way" passages for air. It can ONLY go from muffler to bottom of the tank and ONLY from top of tank to muffler to release pressure upon slowing down etc.

rcbence

Hey guys, im looking into buying the newer 4.6 savage. Ive done lots of research to make it go smooth as possible. This idea seems very good. Im surprised its not getting more replies. Anyone have any long term success with this? On other glow powered rc as well? The shortening thing makes sense too, and seems everyone likes it. Although this makes more sense as a almost complete fix. I modified the cheaper one way valve i already happen to have from trying it on my plane awhile back, which didnt work because of the high pressure when returning throttle and filling up the carb. Anyways i dont seem to have a real problem with the planes for some reason with HTL. My question is, can my fuel tubing be nice and long for the upside down moments and still be effective at pressurizing everything nicely? Reason i ask is that the other mod says to shorten both exhaust pressure line as well as fuel line. Fuel line because it supposedly requires less pressure because of less friction and all.

rcbence

..

1QwkSport2.5r

I don't know savages at all, but if the new tank is taller than the old one, it stands to reason that you would have gravity working for you as well as muffler pressure because there is effectively more fuel above the pickup going to the carb which increases the pressure at the pickup. This could cause problems if too much of the tank is above the carb. I doubt it would be too much of a big deal on a monster truck though.

As for the shorter fuel lines - longer fuel lines usually work within reason, however the longer they are the harder it will get for the engine to pull fuel. For best fuel draw and needle setting ability, you want the tank as close to the engine and have the fuel and pressure lines as short as possible. I run LST2 trucks and run the fuel and pressure lines "just" long enough. Plenty of time to run and flip it back over and clear the air bubble.

Hope that sheds a little light on the subject?

[email protected]

I read through this so many times and did not understand but now I do. The pressure line feeding into the bottom will always be subject to the pressure of the fuel in the tank. When tank is over half full, surface tension is high due to higher surface area and thus the pressure line has to overcome this, which causes the pressure entering the tank to be regulated in a way. In the same way when the tank is below half and has reduced surface tension due to reduced surface area, the pressure line has less to overcome when compared to a full tank and can let more pressure through. This mod allows for the pressure to be consistent and directly proportional to the exhaust pressure and NOT the tank level. I'll be ordering the parts and reporting back. I have tried different things such as the header tank with no success.