half tank lean

[savagecre]

What is this exacly Ive got alittle over 1 gallon through my savage25 ltd ed and Ive noticed that on a full tank and just strarting up its slugish for a little bit but at like half tank its rippin and more responsive I dont have my temp reader here so i cant tell if the temp is rising or not is this the half tank lean that you guys have been talkin about ?

[Xjeepguy]

Yep, that would be it. Be careful though, the temps can get way over 300 towards the bottom of the tank. I recommend a mid tank, but thats just me.

[savagecre]

Yep, that would be it. Be careful though, the temps can get way over 300 towards the bottom of the tank. I recommend a mid tank, but thats just me.
thanx but what is a mid tank? sorry Im new. can I just go down to my lhs and get one?

[Xjeepguy]

No, it is a mod you have to build. Basically it is putting a 1/8 scale buggy tank in the radio box, and mounting the throttle servo next to the engine. If I can find some pics of my old savage, I will post a pic or two in the morning when I get home.

[guest]

from what i know, u can also get a newer stock tank that does not have a primer pump. this seems to help cut down on the mid tank lean issues.

i've also heard of people running longer pressure lines or adding a fuel filter to the pressure line.

[savagecre]

what is exacly happening is more air being drawn into the motor if i new what was happening I could better fix the problem Im trying to emagine whats happening but confused????/

[jrstorm]

there are a few design flaws causing the half tank lean problem. some never have it and some its really bad with. im not really sure why that is, i know the newer primerless, and rear fuel pickup tanks really helped[ i have heard of some with the old tank not ever having the problem.]. others have changed the length of the pressure lines and had success getting rid of it. i tried all those mods to git rid of it and none worked for me. what i finally figgured out , is the tank when full the fuel level is above the carb inlet. so with the increased tank pressure[tank being full and running wot the engine is putting out a lot of pressure and the tank cant hold it all]at full helps to flood the engine. then it needs to be leaned to compensate for the higher pressure. then when the tank is below the carb , around the seam in the tank[1/2 tank] there is room for the pressure inside the tank and fuel flows normal again, which makes the carb settings be too lean.but as the tank emptys it gets worse as the air volume is increased and pressure isnt . my truck would continue to lean itsself out through the reat of the tank. most trucks do this but nownere as bad. most have the tank mounted so that the full level is just at the bottom of the carb inlet, so its not as noticable,if any. the header tank and the mid tank mods are the only real fix for the problem[ at least out of everything i tried]. i mounted a small tank in the back of my truck and i put it lower than the carb and it really helped, the header tank is full all the time and dosent change flow or pressure going to the carb. it makes the engine run a lot more consistent, through the entire tank of fuel. my first set up of the heaer tank i mounted it on the side of the roll bar. it fixed the problem but was easily destyoyed in a roll over with the body off .it also would flood the engine very easialy while it was running causing me to have to lean the carb more than needed and would make the engine run hot. that way really narrowed my tuning range.[ from the point of being too rich and flooding badly and too lean and running too hot] the header is a bit of a pain to fill on the first run and draining it after the last run.i only run it empty if i am done for the day then i have to pump out the little bit left that the engine wont pickup.its worth the little extra work needed on the first and last runs because it really works.here some pics.http://i16.photobucket.com/albums/b42/jrstorm/DSCF0019.jpg
http://i16.photobucket.com/albums/b42/jrstorm/DSCF0018.jpg
http://i16.photobucket.com/albums/b42/jrstorm/DSCF0017.jpg
http://i16.photobucket.com/albums/b42/jrstorm/DSCF0003.jpg

[savagecre]

RIGHT ON thanx jrstorm hey them wheels look good man got to get me a set still tryin to save up the money.... I'll be makin a tank next .

[savagecre]

So let me get this the pressure coming from the exahust pipe hose to the tank is very high at WOT causing the fuel to less'n it's flow to the motor and getting worse as the level goes down... If that is correct then wouldnt an inline pressure flow control help that without the other tank..at my job we have little flow controls for air pressure up to 120 psi. we use them to control the rate that the air moves through they come with barb fittings that fit the I.D. of the fuel line ........cuz if Im under standing you correctly then this should work also??

[jrstorm]

the pressure is part of the problem. fluid seaks its own level. so in the savage tank the fuel is above the carb at full tank and then below the carb after half tank. so the tank position and pressure inconsistencys together are causing the problem.i dont know how high the psi is at wot in the tank, but i played with the tank and blowing into the full tank with a old line to see what happens. it really dosent take much pressure to make the fuel flow. the pressure needs to be automaticly addjusted for the flow to be consistent. what the header tank dose it it is a constant supply of fuel. when the tank is filled by the main tank it stays full throughout the entire run time til the main tank is emptyed.so the pressure changing really dosent affect the engine, and it never leans out. adding a pressure fitting might help but it has to be addjusted as the tank emptys. the header tank cost me 3 dollars and it took a few mins to install it and eliminated all running problems caused by the poor tank design. the pressure in the line from the exhause isnt the entire problem it dose aggrevate the problem though. iv heard of people using longer lines to help, iv also heard that using a diffrent pipe also helps some too. iv even heard of adding an inline fuel filter with the filter removed to act as a pressure chamber to help with the problem. i tried all of these and none worked for me.the header tank fixed the problem for me because it consistently feeds the carb a constant fuel supply , and the header tank isnt affected by any changing pressure from the exhaust.,since the pickup is always flooded and the tank is small enough that the pressure provided by the main tank is always keeping the small tank full. the engine never really has a chance to empty it until the main tank is empty.even then it really never leans out til its pretty much empty.what i do when im done running for the day is, i let the engine use all the fuel it can from the header tank.then when the tank[header ] gets pretty close to empty then i let the truck sit and idle, then i turn the header tank so it has all the fuel around the pickup in the tank. then i let it run til it sucks up all it can. it leans out a little but not enough to hurt anything.it works pretty good and gets out all but a few drops of fuel. i hope this helps.

[garagedoorguy]

No offense Jrstorm, but to make a long story short. The header tank, or mid tank, supplies a constant supply of fuel to the carb allowing it to not have to pull fuel, it is just supplied with it no matter what is happening with pressure, and doesn't care if the fuel is sloshing in the main tank. I have seen air bubbles in the line leading to the header tank, but never make it to the carb line. It also supplies it with fuel when it is flipped over, and adds a little runtime. Do it Savageacre, your engine will love you for it. I bash in rough country, so I mounted mine inside the carry handle so it don't break. You have to turn the air filter 90 degrees to the left( if you are looking a the rear of the savage), but you gotta watch it or it will rub on the spur. I hope this helps, and don't make mr storm upset because he helped me through this same ordeal with mine.

[jrstorm]

no prob garagedoorguy. just trying to help.i have noticed the things you mentioned also. there are so many diffrent theorys and versoins, and things that have worked for others and not for all. some have not ever even had the problem.you pointed out and explained what i was trying to, only in simpler terms. the fact is the header gives a cleaner and more constant supply. it works where other ideas dont. i think if hpi adapted this design it would make a lot better truck for everyone.

[garagedoorguy]

NO KIDDING. The Warhead comes with a header tank. DUUUUHHHHH. You can look at the warhead, and see the similarities to the savage. Maybe HPI leaves a little "hobby" in it, but nobody will make me believe that they never came across this problem while testing.

[savagecre]

yeah It helps I get how the header tank works especially if it stays full untill the main tank runs out.. it acts like a buffer between the main tank and the carb cool my lhs dosent know anything about it. then when I read on this site which is the best site around I think No sooner then I was reading about it , it started acting weird.

[garagedoorguy]

Take what the guys at the hobbyshop say with a grain of salt. They will send you out the door chaising your tail in a heartbeat.

[jrstorm]

one of the lhs around me have never been able to get rid of the half tank lean prob. i showed them my truck and they were really impressed and are going to start installing the header tank when they have a truck that comes in and cant be fixed.my truck didnt do it til almost a gallon was ran through mine. i dont know what the real problem is but the header tank really works.

[garagedoorguy]

Ok let's put it into easy terms. The savage like's fuel like a cold beer. When it's full it's happy. About half way down, it wants to just chug it down, and on to the next tank, or beer. lol. If it has a constant flow, it delays the chugging factor. Hope this helps.

P.S. Do not take this as valuable information. lol.

[jrstorm]

heres some new pics of the header tank mod;http://i16.photobucket.com/albums/b42/jrstorm/DSCF000300.jpg
http://i16.photobucket.com/albums/b42/jrstorm/DSCF000100.jpg
http://i16.photobucket.com/albums/b42/jrstorm/DSCF000400.jpg
http://i16.photobucket.com/albums/b42/jrstorm/DSCF000200.jpg
http://i16.photobucket.com/albums/b42/jrstorm/DSCF000600.jpg
http://i16.photobucket.com/albums/b42/jrstorm/DSCF000500.jpg

[savagecre]

Yeah hey I dont want to make any body upset last thing on my mind. Just have to know why its who I am. I payed 580 out the door for the truck starter kit extra set of rims and tires fuel dont want to have to spend 100 to 200 for a motor that fast I've only had this truck like one month got one gallon one quart through it now and well like I said I HAVE TO KNOW WHY IT IS on enything so THANKS YOU GUYS ROCK ...

[jrstorm]

no problem. iv had my ss 4.6 savage since thanksgiving. i was really dissipointed in the 4.6 engine from the start. the pull cord broke on the first pull. all my other trucks have been on the bumpstart. so i had no real experiance with pullstarts[ enough to hate them] so i was a little dissapointed in the pullstart. well after i got all that worked out i pretty quick found out about the half tank lean problem. im like you i want to know why somthing dose what it dose. i tried all kinds of mods to fix it. most info on the problem i could find, all pointed to changing the pickup position of the tank[mid tank mod, and the header tank] all the other mods were just good gueses at the problem. some of the other mods help some people but not all . i tried every mod i could find, and none helped me. i first thought it was a header /pipe combo that was causing it[ tried a diffrent one -no affect] then i was reading about someone doing a air pressure mod and i tried that it didnt work. [ they take a clunk and a pice of antena tube and put the tube on the nipple where it goes into the top of the tank and put the clunk on the other end of the antena tube and let it go to the bottom of the tank . they say this changes the pressure in the tank ,but all it did for me was put air bubbles in my fuel.-like an aquarium air stone] so i really started looking at the fuel tank design and saw where the header tanks solved the problem. so i tried it and it worked. so i have had a crash coruse on fixing savages . glad to help..

[jrstorm]

oh yea, i have been thinking the engines only lasting for 3 gallons or so, might of been because of the lean problem.my first engine was doing it bad and didnt really notice it til i started to lean for power. i had to keep it really rich at the bottom of the tank and lean it out to run at a full tank. even the rich settings at the bottom half of the tank made it still overheat with any hard bashing. i think it helped wear out the engines quicker. especially since i had to tune it all the time. the second engine lasted a gallon longer than the first did. but i had added the header tank at maby 1.5 gallons. the picco was just a problem from the get go. it was having problems in my other trucks too, so i really think i just got a bad one and need to send it back to ofna for replacement. i wouldent worrie about the engine , the .25 engine is an excellent engine and is very reliable. the 4.6 the 2 i had were problems but by the time i got the header tank installed on the second engine i think i had already done damage. so i really cant fairly criticize the 4.6 engine. but the main bearing went on both 4.6 engines i had, and thats nothing that the tank problems would of caused. when i finally took the last 4.6 engine out for good , it wasnt running. it would die very quickly or wouldent run at all. the problem was the main bearings were skipping their races and jambing up the crank and stopping the engine or making it stall and not start easy.what engine do you have?

[savagecre]

you know its probably the manufactures way of makin money they rely on us buyin another motor from them lol Ive got the 25

[jrstorm]

yep i agree. my buddy and i were talking about that this weekend. the mfg would rather us having problems. my lhs told me that they make more money in parts than on trucks sold there.so thats probally true of the companys too. if the trucks were indestructable then they would loose money.

[Mesquite]

I’m having a similar problem with my savage X 4.1. After reading this thread I realized that the problem started after I installed the optional exhaust cone. Could this be causing my half tank problems? It would make sense that it is causing more pressure in the pipe as it restricts the exhaust flow resulting in a more erratic fuel flow. I’ll try removing it tomorrow.

[jrstorm]

one thing iv seen thats part of the problem that i havent figured out yet, is the exhaust. iv heard of people who have changed to all copper lines and the problem being fixed.iv also heard people have put a empty fuel filter in the pressure line and it fixed it . iv tried the filter in the pressure line and it didnt work for me. iv also heard of people changing the exhaust and it fixed it. it didnt work for me either. my truck didnt do it til i was into the second gallon of fuel and it was getting worse the more i ran it. i had to do somthing and nothing i tried worked for me.try changing the cone out of the pipe and see what happens. the exhaust pressure is part of the problem with it so the more flow to the tank the better. good luck...

[Mesquite]

Removing the cone helped, it made the truck drivable but there is still a problem. I have a spare fuel filter so I'm going to try that. I hope it works, if not I’ll be building a header tank.

[savage spares]

hi guys where can u get these littel tank mod from i need 1

[Hawkeye]

It's a homemade mod, check out the thread "half tank lean again". there are a few links there to tanks that work.

[sleeper341]

i still fail to see how the header tank helps. surely the pressure from the exaust to the fuel tank still fluctuates and the amount of pressure needed to keep a steady flow of fuel from the fuel tank to the header tank and on to the carb would be the same as needed without a header tank in the system?

but if it works i'll try it, the only problem i have is that to drive/race or bash on UK offroad tracks you are not allowed modified fuel tanks so i'd have to take the header tank out and retune before i could go on a purpose built track :(

oh and just to clarify - the best position for the header tank is below the carb needle or above?

Thanks

[jrstorm]

you are right . the exhaust pressure is still going to flucuate. but having the header tank installed makes the engine get a constant supply of fuel to the engine nomatter how whe pressure changes. the pressure is what delivers the fuel. the stock tank shape is more of what causes the problem, because the carb has to work harder to get the fuel to flow to it correctly. the header tank stays full all the time so the carb has a constant resivore to draw from. when the main tank goes below the carb height it causes the engine to get leaned out, but with the header tank the engine never sees this so it dosent lean out. also when the stock tank is full it is above the carb which makes you tune it leaner to get it to run correctly ,so when the fuel is nolonger being forced to the carb[because of gravaty] it gets leaned out. the best place iv found for the header is behind the shock tower. it is close to even with the carb, you still dont want it to be above the carb too much to keep it from flooding the carb. also this isnt a mod for more speed or power ,or really even longer run times, its simply for making a bad designed tank work correctly. there are a few trucks out that come with it stock

[sleeper341]

Thanks JR, that makes it a bit clearer, i wasn't doubting it worked, just trying to understand how. Must be a pain to fill the header tank before a days bashing though. i see yours has a lid so you can fill it, but the ones i've seen seem to be sealed, its gonna talke a fair few gentle pulls on my starter to fill it! :confused:

[sleeper341]

just looking at the tank recommended on one of the posts - http://www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXLRH1&P=7 do i run the fuel line from the main tank to the top of the header and then from the bottom of the header to the carb or run main tank to bottom of header and top of header to carb?

the first way round makes more sense to me but i thought i'd check :)

[jrstorm]

what i do is i use a primer ball filter then run from the main tank to the top port on the header ,then i run the lower port on the header to the carb. what you have to do on the first tank is remove the line off the carb and hold it in the air above the truck.fill the main tank as normal. then use the primer ball to fill the header tank. if you dont hold the carb line in the air it will flood the engine and never fill the header tank.i usally can prime the header tank almost full. then i reconnect the carb line and start the engine as normal.usally by the time i get the body on the header tank is completly full. i usally run the truck til the main tank is empty that way i dont have to refill the header tank. i usally remove the carb line and plug the exhaust pipe to turn it off.if you dont remove the carb line on shutoff then it will flood the engine badly for the next start up.on the last run of the day i let the engine use all the fuel inside the header tank so it dosent sit with it full til i run the truck again. it sounds like a pain but it really isnt and its worth it because it really dose work to eliminate the half tank lean problem. it also makes the engine run a lot better and stays more consistent most of the time. i hardly have to mess with the carb settings. i hope this helps.. john...

[HPI_Savage25]

Know what's weird... I don't know what yall are talking about... I've never had the problem.... wonder why not.. I've used 2 gallons

[Hoppedup Savage]

they put a header tank on there and it keeps it from leaning out when you have about half a tank of fuel left hence 'half tank lean'

[jrstorm]

some people get it and others say they never have had it. i dont understand why, the only thing i can figgure is maby if you are tuning for optominal preformance or staying on the rich side. my orginal 4.6 engine didnt start doing it til i got to the almost 2 gallon mark. it was bad and did it noomatter how rich i set the carb. it was so bad that the engine barely ran til i got just at 1/2 tank, then it ran good but it was a real pain having to tune the carb all the time.oh well if you have it do the header tank mod and it will fix it .

[Xjeepguy]

Know what's weird... I don't know what yall are talking about... I've never had the problem.... wonder why not.. I've used 2 gallons

What kind of temp gun are you using, and where on the motor are you checking the temp? The reason I ask is because the 1/2 tank lean is a design flaw, and it should effect every savage.

[HPI_Savage25]

Well i go to my lhs since he knows me and my dad reallllllllly good. so he lets me drive it their and testes it... he testr on the head

[Chaos]

does the mid tank mod help this out?...because you actually putt the whole tank above the carb inlet.When my motor starts leaning it's self out i know it's time to come on in for fuel and a little cool down.....so it didn't really pose to much of a problem for me yet.

[jrstorm]

from what iv tried. i didnt like a mid tank because it cut down on the ammount of fuel i could run.and putting tha entire tank above the carb made my truck get flooded very easialy. and hard to start. the header tank mod is cheap and easy and dosent change the electronics box to make it work.i think i have 3 dollars into my header tank and maby 8 in a filter/primer ball , and i didnt have to mod anything to make it work. i just attached it to the rear shock tower with a zip tye. its really easy to do and fixes all running problems due to the bad tank design.

[Xjeepguy]

If the mid-tank is done right the tank is no higher than the stock tank. The design flaw is in the stock tank itself. Brcause the tank changes shape halfway down, the pressure changes when it gets to that "ledge" on the inside of the tank. At that point there is alot more volume to fill before applying pressure to the fuel. Adding a mid tank has nothing to do with the height of the tank itself, but the reason it works is it gets rid of the troublesome stock tank alltogether and replaces it with a properly designed tank. My next mid tank will be using a MGT tank so I dont lose as much run time.

Well i go to my lhs since he knows me and my dad reallllllllly good. so he lets me drive it their and testes it... he testr on the head

I strongly suggest getting a cheap lazer temp gauge like a duratrax flashpoint, and checking it periodicly throughout the tank. If you are running a savage with a stock tank, you have the 1/2 tank lean. You wont know by the way it's running, only by the temps. And when you check your temp, make sure you are checking it at the glow plug, and not the cooling head.

[Chaos]

Kool...thanks XJ..makes more sense now.

-Joe

[trashard]

My half tank lean problem is so bad that it almost seems the engine can`t hold a tune.
I`ve gotta go to the lhs tuesday to order some tranny parts and I think I`ll get some larger diam. fuel line and put it between the exhaust & fuel cap and I`ll try to grind out the connector on the exhaust.
I already made the fuel lines a bit shorter and it seems to help but it`s still so bad that I don`t need a temp gauge to see that I got the half tank lean issue

[jrstorm]

yep mine was so bad i had to retune to get it to run with a full tank. it slowly got worse. when i first got my truck it was runing fine then i started noticing it as i was tuning for performance after breakin. i went through 2 hpi 4.6 engines so after i put in the first replacement engine, i went til breakin was over then it started again. then i went to a picco .27 after the second hpi engine came appart, then i didnt see the half tank til i got through the breakin with the picco.mine was so bad after i filled the tank to run again it was so boggy that i had to lean the hsn almost a full 2 turns in to be able to run it til it burned down to half tank.then all of a sudden the engine would start screaming and smoke trali would go away and the temps would rise. my temps would go almost 75 degrees within one lap.it was like someone would turn on a light switch. once i tuned it good for half tank it would run fine. i could fill it only half way and run from there and all would be good. i even would start at half tank but runtimes were cut in half, so id run it til it was almost empty and then refil to half tank without shutting it off . that got to be a pain too.then it started getting worse even at half tank. i dont know what starts it , iv got theorys about it, all dont make any sense ,neither dose the reason it seems to get worse. i even think maby my first 2 engines might of blown because of it.

[Xjeepguy]

Yeah, this is the reason I am very dissapointed with HPI right now. They came out with the savage X, they had an oppertunity to fix their biggest problem but they left that same old tank on there. The other changes were great, but as a brand new savage comes, it is set to self destruct. I have seen temps that topped 400* after running fine at 240* the first half of the tank. It is something that is fixable, but is one of the reasons I no longer have a savage. I loved the trucks, hated the tanks. I despise the fact I have to lessen my runtime to fix a problem that HPI wont recognise. OK, rant over, I will put my soapbox away :).

[toyotatech1]

if the problem is with the design of the tank it self and not where it sits from what i have read. couldent you just swap tanks with some thing that does work.

also how big of a tank do you have to have for a header tank cause i have a old plane tank that looks like the one in the pics i think will work. and where do i get the primer/filter ball. cause i think that i may have exspeirence this with my ofna motor and wwonder if it wikk efect me with my o.s 30 max motor since it is a biger motor wont it take more fuel

[Rake]

Wow great thread I learned alot. I definately have the half tank lean prob and didnt know it.

[savage spares]

http://i39.photobucket.com/albums/e173/K1NGOFBL1NG/savage28stsfinished014.jpg this is how i done my half a tank lean mod