twomanytoys

I was reading all these posts about the half tank lean problems that the savages have. I have 2 savages. A savage X and a Savage X SS. My sons X does not have this problem. Temps stay consistant around 250 no matter if its full or almost empty. My X SS has it really bad. temps when full are about 230 then shoot up to 280 at half tank then slowly go down as the tank gets low. I have read about all the mods from longer lines, ofna tank and mid tank mod, valves, pretanks etc.... One thing that did not make sense was extending the lines. As the pressure drops in the tank you have less pressure to travel into the longer fuel lines thus making the engine run leaner. I ended up making the fuel line as short as possible and my temps dropped almost 20 degrees. It now sits around 255-260 through the whole tank. It would make more sense that the shorter the line the less pressure you would need to push the fuel.

To make sure it was not a fluke I installed the longer line and temps went back up to 280+.I installed shorter line and temps went down. I have been running it with the shorter line all day today and temps stayed consistant around 260. Not sure if anyone else has tried this but I have not read anywhere about shortening the fuel line which would make more sense. Less pressure, shorter line. More pressure, longer line.

Argess

Hadn't thought about the fuel line, but a long time ago I made the pressure line as short as possible for the same reason and that kept the leaning (and temp increase) to an acceptable minimum for the NitroStar 25. When I switched to the OS 30VG, the 1/2 tank lean became more apparent and I did another mod. It certainly seems some engines react differently.

It makes sense to keep lines short as they are fairly small inside diameter and are somewhat restrictive. For exhaust pressure, it is important as exhaust flow back and forth along the line is rather rapid and also is continuously changing as you get "on" and "off" the throttle. IN this case, shorter is better. I hadn't thought this would apply to a line filled with fuel, but it's a very interesting discovery.

Can you please tell us how long the two lengths you used were (short and long)?

Very interesting................


Don't take this wrong, but is there any possibility that your experiment was tainted in any way? For example, was your longer fuel line lying on the hot exhaust pipe? ...or anything like that?



to fuel or exhaust gas flow.

twomanytoys

The long line is 13" and the short is 5". The long line was coiled around the rear tower not touching the exhaust at all. The short now runs in front of the engine between the carb and head with the nipple facing towards the tank. I have been running the crap out of it all day today and its never run better. Temps never got above 265 and that was racing one after another for about 3/4 of a tank. I could have not done that with the longer line. Usually after about 2-3 races its at 280 before I let off and let it cool.

Argess

Well.....good one!!! As I said, I shortened my pressure line, but I never tried the fuel line. Never even thought of it. Too cool! Wouldn't it be funny if all those Savage owners, over all these years, did mid-tank mods, header tank mods, etc., etc...... for nothing?

In case you get any criticizm about: "With the short line, one might run out of fuel quicker, when upside down (takes time to get to the upside down vehicle)." ...just suggest a BIG fuel filter be installed.

twomanytoys

I have put mine on its lit a few times so far and it still takes a bit to stall. I literally ran about 1 qt of fuel today. The most I have run my truck at one time. It ran great. That would be cool if thats all it needed. Anyways Im happy I did not have to do some crazy mod just to keep it cool. I was about to buy the Ofna tank and ebmods mount but did not like the idea of less run times so I tries this as last resort. Im happy with it now.

Vigilante212

The only problem about a short fuel line is when you flip it will starve the engine fairly quickly.

twomanytoys

Not as quick as you would think. Like I posted above I have put it on its lid a few times yesterday and had no quick stalling issues. I had at least 10-15 seconds before it would even start to rev from leaning before I was able to flip it over. I was going to play today also but I have a Spectrum servo that is going bad. Im going to have to take one from my truggy to play.

Parputt537

It is amazing how simple things are sometimes. After reading this and looking at the simplicity I said "Why Not"? So today I went out with my new short, about 5", fuel line and gave her a go. Temp stayed around 240-250 the entire tank. The I did get her up to around 260 twice and that was doing continuous high speed runs both at full tank and mid tank. Started driving normal again and she went right back down to around 245.

The one area where I could really notice a difference and gave me the most evidence that this does work is on my LSN tune. I tune my truck so I loads up after about 10sec. at idle. Prior to the short fuel line my LSN tune would be all over the place. At full tank it would load up after about 10sec., but at half tank and lower than 1/4 tank it would take much longer to load up and would idle forever. To me the consistent LSN tune combined with the consistent temps tells me that this works!

For the people that are worried about lid run time I suggest you run your trucks on the wheels like they were intended

Thanks for posting this twomanytoys!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! !!!!

Argess

Hey...a second guy to try it with success.....too cool!

For the life of me, I can't figure out why it works. The pressure line has to pass a lot of exhaust gas very quickly to pressurize a tank low on fuel, so one can see why a restrictive hose could cause problems. But the fuel line to the carb? Fuel flows very slowly to the carb, so the small inside diameter and length shouldn't matter. Plus as it's filled with non-compressible fuel, any pressure change on one end should mean the exact pressure change on the other end, virtually instantaneously.

But there's no arguing with results. I"m not sure how the theory works, but CONGRATULATIONS Twomanytoys !!!!

I have another mod on my Savage now, but I think I will try this on my OFNA buggy. If it works, I may de-mod the Savage, and try the short fuel line on it too. Now, don't take offense when I say "if it works". Because I am not sure "why this works", there may be a difference with the buggy that isn't obvious and won't allow it to work.

LOL.....I think this is so funny....too simple !!!!

BudBud

It works that way with water, oil, and even gasoline, that is why they have booster stations along the way on pipelines. There is a certain loss to friction along the way...

Argess

Hey Guys....a couple of questions:

Twomanytoys....you said in your original post that:

"temps when full are about 230 then shoot up to 280 at half tank then slowly go down as the tank gets low."

That's interesting.....mine used to continue to rise as the fuel level continued to drop. Any idea why yours seemed leaner at mid-tank?

Twomanytoys also said:

"As the pressure drops in the tank you have less pressure to travel into the longer fuel lines thus making the engine run leaner."

I take it you meant lower pressure as the fuel level went low, but di you consider that the pressure also drops low when at an idle?...see below...

and Parputt537 says:

"The one area where I could really notice a difference and gave me the most evidence that this does work is on my LSN tune. I tune my truck so I loads up after about 10sec. at idle. Prior to the short fuel line my LSN tune would be all over the place. At full tank it would load up after about 10sec., but at half tank and lower than 1/4 tank it would take much longer to load up and would idle forever. To me the consistent LSN tune combined with the consistent temps tells me that this works!"

Do you suppose that the increase in temps was due more to a lean idle than WOT? I have always assumed that the Half Tank LEan problem was more of a high rpm realted issue. Could it be an idle related issue?

ps: in case you are wondering, I have an inquiring mind. That's why I am babbling on so much.....LOL.

Parputt537

To answer my part of your question: I do not think so.

Like I said, the LSN tune would change as the motor leaned due to the half tank lean. I am a obsessive compulsive type so I am constantly checking temps and tweaking settings. One think I really pay attention to is my LSN tune because I like my truck to jump off the line. I have found that the best LSN tune will idle for 10-15 sec. before loading up and start to flood. When the tank would reach half full the overall tune of the truck would lean out, temps would go up, and my LSN idle time would increase to 30 - 40 seconds before it loaded up or it might not even load up at all. At below a quarter tank the LSN would go very lean and it would never load up. The temps at idle were always manageable. WOT is what caused the real spikes in temp. My motor always cooled at idle as I never ran the LSN so lean that it would not. That is just not good for the motor and eats glow plugs for lunch.

I checked my temps a hundred times this afternoon and they stayed right around 240-250 except during the continuous WOT runs at full tank, half tank, and quarter tank. My LSN tune stayed consistent and the motor would load up right at about 10 sec. and start to gurgle. When I would pull in to refuel or make adjustments the temp would quickly drop.

So no I do not think any of this is idle related. With the longer fuel line my entire tune HS and LS would lean when it reached half tank. Evidence of this was the idle time increasing at half tank. Longer idle time = Lean LSN, Shorter idle time = Rich LSN. For it to lean out without me making any adjustments tells me the half tank issue was the cause.

twomanytoys

I cant answer why this works.All I know is that i was getting fed up with the constant half tank lean adn really did not want to spend the money to get a smaller tank or mid tank mod. All I could think of is a shorter line would take less pressure to move teh fuel to the carb so as the tank pressure drops you still get decent pressure through the shorter line. I ran the truck all day today watching the temps and tehy have never been more consistant. Idle is great and I was able to put the screw driver down because I did not have to tweak it after every half tank. It was getting to the point where I put the temp gun down and did not touch it for about 4-5 tanks. It starts easier and has pretty much the same power through the whole tank. Prior to the short line it was a dog for teh first half then it would run like a raped ape. Now it runs like a raped ape through out the whole tank. I dont know teh physics of longer vs shorter. All I know is it is working great for me. I know every engine is different but one thing for sure is that most all savages have the mid tank lean. Some more than others. It cost me nothing to try this. No more frustration. Temps never went above 265 today and it was 85 degrees outside.

Argess

Don't cut yourself short TwoManyToys (hehehehe...there's a pun in there somewheres...). What I mean, is give yourself some credit. Accrding to the link below, you were correct in assuming the length of the fuel line affects flow rate and engine tune. I would have thought the fuel flowed too slowly for the line to affect it much. Guess I was wrong.

Here's a cut'n'paste from the link:

The line from tank-to-carb can be lengthened or shortened, also. Its length can impact the running of the engine in a similar fashion as the back pressure line. The fuel delivery system is a self leaning system. This means that as the tank gets closer to empty, the engine will start to run leaner. If you shorten the line from tank-to-carb, you can counter this tendancy a little. The shorter line will move fuel to the carb more easily and at higher "flow rate". This increased volume of fuel delivered will cause the engine to want to run rich. By lengthening this line you create the exact opposite affect, and the engine will tend to run lean. As with the back pressure line, working with extremes of length or shortness can impact the performance beyond your ability to tune the engine.

Here's the link:

http://www.rcnitrotalk.com/forum/showthread.php?t=1199

If the link gets removed, just Google "Stupid Fuel Line Question"

Argess

OK....I just tried it with my OFNA Ultra (which has a NitroStar 25 in it, by the way). Here's my results:

1/ I had already shortened the pressure line, so the half tank leaning wasn't all that bad, but it was there.

2/ I shortened the fuel line from the tank to the carb as short as I could (less than 4 inches incuding filter). It had been long enough it went around the cylinder head and back to the carb in front.

3/ I then drove consistent hard driving through tall grass measuring the temp every time I went by. After the engine had warmed up, the temp stayed constant and the engine didn't lean out as the fuel level dropped.

4/ I noticed my top end was still in tune from the last time I drove it, but my idle was rich and it bogged on launch. I then leaned the LSN a bit over 1/8 turn, re4filled with fuel and drove another tankful before the engine cooled down.

5/ Same consistentcy with temps. Worked perfect. About 10 seconds bfore it ran out of fuel, it exhibited some lean running, but at that point I'm sure it was sucking air bubbles as there was no fuel left in the tank.

AGAIN, CONGRATULATIONS TWO MANY TOYS,...you've got a winner mod here. An absolutely free mod that takes seconds to embody!!!

twomanytoys

Thank you Argess. Something so simple that has been overlooked for years. Thanks for the link. That would explain my theory of long vs short. I put about 1/2 gallon on my truck this weekend and it was great. I still check temps every so often but thats just me. I like to know everything is where it should be. There are soo many other sites that would need this type of info for the savage. It sure would save alot of money in trial and error to correct the problem. If anyone tries this I would like to know the results. So far I have almost 10 people that have tried it all with success.

Parputt537

I'm going give my Savage X and LST2 a good workout tomorrow at the local BMX track. I only tested for a short period the other day so I will post the results of my "extended" test tomorrow afternoon sometime.

Parputt537

OK, I am convinced. Went and ran three tanks through the Savage today. First tank I ran the truck pretty hard doing WOT runs and some jumps. Temps stayed between 240 - 250 until I got below a quarter tank then they came up a little which is normal for any RC.

Second tank I just kind putted around going over the wooptie doos and farting around. Temps stayed between 230 - 240 until I got below a quarter tank. Again very normal for any RC to lean as the tank gets empty.

I also kept a close eye on my idle times again. Naturally I was bringing the truck in quite frequently to check temps and the idle time stayed at a consistent 10 sec. before it would load up and start to gurgle.

So, in my opinion, this is a great, simple, cheap, and pretty brilliant fix for the half tank lean!!!!!!!!!!!!!

Major props to twomanytoys for thinking outside the box and also for passing this along to the community.

twomanytoys

Woodmandan2

Heh Funny, Works perfectly on my savvy, On my Jato it'll hardly run at all with direct fuel line to the engine, I gotta have it coiled up. Thank You twomanytoys!!!
woodmandan2

twomanytoys

I had 2 jatos adn never had any leaning problems. The reason why it wont run with shorter line on teh jato is because it runs very rich,. They extended the lines on them mor for tuning but also they will expect that you will spend alot of time upside down.

beer=food

Well LOL, isnt that common sence and physic's, dont any of you guys ever think about it ?
Never wondered why most truggies come with really short fuel lines ?
He should not have had to tell you guys this, its the sort of thing you should know, when cornering, another known leaning effect, lieing fuel line flat in loops has the same effect leans it out , but if you loop it verticaly, it will not have that effect, same with the exhaust system, any extra extractor length = less power, waste of energy, do you guys run 1/10 fuel lines or 1/8, theres a few different sizes, get the biggest for the fuel line, smaller for the backpressure, a great place for really cheap fuel line is a motor bike shop.Get a 50cc motor bike engine filter, man upside down idle for 5 minutes !
Well done thread starter, it seems you have woken a few guys up, that may have been complacent about the nigglies and fiddlies of nitro !
Some im sure who would have been posting at a later date, ''stupid thing wont hold a tune !'' LOL !

rcnitrohead

Haha, I cut my fuel line today and it's a lot less noticeable, nice one twomany

twomanytoys

Run it as short as you can and run it in front of the engine not the back. I turned the carb nipple facing the tank so the line is pretty much direct straight from carb to tank.

I have tried running the line as short as I can behind the engine with the nipple in the stock position but it does not work as good. Its still too long that way. Line needs to be about 5" long.

rcnitrohead

Thats how mine is right now