full tank sluggish

[Want to run?]

I was running the savage today and i noticed my 3 speed transmission was not changing gears properly. It only change the first 2 gears. Then i also noticed when it was about 1/4 tank or lower it would then shift 3 gears. So basically the savage would give it all it got if its a 1/4 tank or lower why is that? And everytime i would fill it back up after the tank was empty the first take off was very sluggish then half tank it would pick up?

 

[Xjeepguy]

Welcome to the savage's infamous 1\2 tank lean!!

I recommend a mid-tank, but if you want to keep the stock tank, you will have to lean it out at full tak, then richen it up at 1\2 tank to keep from overheating.

 

[Jeepguy]

Can you explain what the mid tank mod does to alleviate this problem? Why would the placement of the tank have anything to do with a lean condition? I've been noticing this lately, and I'd like to fix it if possible. Thanks
Vinny

 

[RLM]

What you described is not the half tank lean issue that everybody has if its not changing gears from a full tank to a quarter tank (not half hence the name half tank lean issue) then that is not your problem!!! The half tank lean thing i find is overrated its not that bad that you need to butcher your truck and zip tie some ugly tank to your truck almost every header tank i have seen looks UGLY!!! I think it may be something else

 

[savagekicknmaxx]

When you have a full tank lean it out slightly and see what that does if it its still don't shift 3rd keep leaning it just slightly till it does, but also make sure its warmed up before hitting it hard, or it won't shift to third till its warm and ready to go.

 

[RLM]

Thats exactly what it sounds like he is set too rich so the engine cant get up to operating temp until 3 quarters of the tank is gone just after the half tank issue which is leaning him out and bringing the temps up i would like to know his engine temperature throughout this whole process is???

 

[Xjeepguy]

What you described is not the half tank lean issue that everybody has if its not changing gears from a full tank to a quarter tank (not half hence the name half tank lean issue) then that is not your problem!!! The half tank lean thing i find is overrated its not that bad that you need to butcher your truck and zip tie some ugly tank to your truck almost every header tank i have seen looks UGLY!!! I think it may be something else

It IS the 1/2 tank lean issue actually, If he is rich on the first half and runs perfect on the second half, whats gonna happen when he makes it run perfect on the first half? Its gonna go real lean after 1/2 tank. I've been through it many times before.

The placement of the tank has nothing to do with it, it is the shape of the stock tank. When the fuel goes below the ledge, the pressure against the fuel changes, thus causing the change. The mid tank not only cures the 1/2 tank lean, it also helps the truck not push so much in the corners, thus curing 2 problems at once.

Telling him to lean it out would bring his temps on the 2nd half of the tank over 300*. The mid tank and haeder tank mod are 2 different things. A proper mid tank is one tank and nothing should be zip-tied.

 

[wullie]

can guys reccomend somewhere to get a mid tank from?

 

[jrstorm]

thats exactly what happened with my truck. it truly is the half tank lean problem. what is happining with your truck is you arent real lean yet. [you didnt provide temps] it sounds like it is real rich at full tank then its leaning out some[due to the bad designed tank] and then it is running better and allowing the engine to rev high enough to let it shift into 3rd. what happened to me was id tune for power with a full tank then when the tank dropped below the half tank mark then the carb settings would be way too lean and then the engine would overheat badly. the problem can be fixed with tuning . tune it to run good with a full tank then when it starts to lean out[ if you can see it when it happens]then richen it back up and finish the tank. but that gets to be a pain and you will wear out the hsn o rings.[ i did] what mine did was it first did it a little then it got a lot worse. at first mine only needed minor 1/16 th turns then eventually i was turning it in and out almost a full 2 turns. i tried replacing the tank [thinking it was cracked] replaced all lines and even trying diffrent length lines . i even replaced the stock 4.6 carb for a new one. i ultimatly think it blew up the first and second hpi 4.6 engines i had. [all 3 hpi 4.6 engines i had blew up due to leaning out and overheating problems, they also all failed their main bearings.] i would have the problem go away with new engines til i had broken them in enough to start tuning for performance. the fix i found was pretty cheap and easy . i bought a new engine and installed a 4 dollar header tank. i tried several diffrent things and the header is the only thing that completly eliminated it for me. i even had our lhs see my truck and they started selling the header tank kits with every savage they sold and said it works. heres a pic of my setup;

 

[jrstorm]

what i think happens with the stock tank is that the shape of the tank changes [because of the shelf]as the tank empties. so the ammount of pressure that the tank sees from the engine changes too. as the air volume in the tank increases the pressure form the engine dosent increase anymore than it did at full so then the engine has to try to pull the fuel from the tank instead of it being fed by the tank.also when the tank is full the tank level is above the carb so it feeds the carb from a little gravaty fed and then when the tank level drops below the carb gravity cant feed it like it did at full and the pressure from the exhaust isnt enough to push the fuel up to the engine so the engine leans itsself out. the same thing happens with real boats. the engines[outboards] have a min requirement of how far away from the tank pickup they can be mounted. if it is out of the spec then the engine will lean out due to lack of fuel supply.the hpi savage tank is a perfect example of that. the mid tank mod gets rid of the tank level being below the carb and solves the problem. i don't like the mid tank mod because i use rechargable aa batts in my trucks . so i would have to disassemble the front to get to my batts every time i needed to recharge them.the mid tank mod is a good one but the header tank works great and actually increases my run time some.

 

[savagekicknmaxx]

I don't really have any issues with the half tank lean issues on my savvy, but of course I moniter my temps alot and if it starts getting to hot from hard runs or long runs I either run it slow and let cool off or richen it slightly. You can use another tank, I still have old t-maxx I could the tank off of it to make a headertank.