MotorBreathLT1

I use to be really goos at tuning these things back in the day, but its been a while and this little issue with my 4.6 is getting the best of me.
I have the hsn and lsn tuned in well, tho a tad rich, but only while the tank is full. Once I get near half a tank, it bogs off the line from a dead stop; the less fuel in the tank, the worse it gets.
I know of the half tank lean, and maybe that's not meant to be taken literaly but it doesn't feel lean, but more so rich.

I've played with the needles, checked for leaks, sealed the engine, used less fuel line and popped in a fresh plug. Help?

Be gentle.

llkoolskillet

change your pipe to an 086. also check your fuel tank for any kind of leaks, or just by a new one.

mubus

yes the 086 helps alot
I have it my xl and the lean is not that bad and temp is pretty consistent
but its a good idea to go for a tank mods of some sort like uniflow or ofna tank mod or midtank mod

this may help
if you tune it for optimal performance at full tank when it goes to half tank it go even leaner and when it's lean it causes something similar to bogging and the engine will struggle and will sometimes shut off...

MotorBreathLT1

Can you link me to these tank mods?

mubus

hmm this is mid tank mod
http://www.youtube.com/watch?v=me7TBLA6HS8
there is more parts to this but this is part 1 (this requires alot of fabrication if you don't have the flm chassis)

and 125cc ofna tank mod
hmm just go to google and type in 125cc ofna tank mod and you can probably see a picture
the fuel tank sites where the old tank is but the way the tank is shaped you won't have the half tank lean, but you lose 35 cc capacity which is 35ml but thats not alot cuz if ur bashing ur refueling anyways

for uniflow mod try
http://www.rcuniverse.com/forum/m_7430203/tm.htm
for this mod go to the link and it will explain everything

Argess

Some engines don't seem to suffer from half-tank-lean,, although most do. So it's wise to start with simple things first:

1/ Make sure engine is warmed up before tuning.

2/ Tune at 1/2 tank of fuel.

3/ Shorten pressure line from muffler to tank as much as possible.
Shortening the fuel line form tank to carb can help, but I have no idea why.

4/ If the above fails to satisfy you, then do one of the half-tank-lean mods

sharkattack99

So what about that half tank lean mod that stops it? Is it just cause the the tank u use is wider and not as deep as the savages tank? So it doest get the chance to go lean at half tank?

mubus

the savage fuel tanks remsemble an L when fuel reaches half the surface area for which preasure can act on the fuel itself becomes smaller then when it was full... so if you switch to another tank where the surface area is constant from top to bottom there is no half tank lean... because pressure acting on the fuel is always even.
also a tune pipe that has a greater back pressure helps
on my savage xl the stock pipe doesn't give much back pressure ( i think 1psi) so i switches to 086 ( give 2 psi) and it helped alot to a point where it only semi noticeable and it really brought my k5.9 to life!!

sharkattack99

so what fuel tanks are more constant? any recommendations? part numbers or links would help.

Argess

Basically, half-tank lean is caused by "at least" these two problems:

Static: As the fuel level drops, the pressure of the fuel to the carb drops. Not by very much. In fact, very, very little...but enough to make a difference. The shallower the tank, the less of a problem this is.

Dynamic: As the fuel level drops, it takes longer for the pressure line to build pressure in the tank when you go from idle to WOT. Reducing the restriciton of the pressure line helps a great deal, therefor shortening it is one answer that will make a noticeable difference.

Other notes:

1/ Different exhaust can help. Anything to inrease the muffler pressure helps make the static problem less significant.

2/ The engine doesn't really lean out at 1/2 tank. It leans out constantly as the fuel level drops. It's because it gets noticeable at around the 1/2 tank level that the problem gets its name. So a tank 1/2 the height as the Savage's tank would appear to cure the problem.

3/ Soime people have had good success meerely by shortening the pressure and the fuel lines to a minimum length. I'm not sure why the fuel line to the carb would make any effect, but apparetnly it does. The problem with shortening that line, is that if you have a flip-over, the engine often stalls before you can get it right-side up again.

4/ The modifed uniflow mod (link above in Mubus's post) attacks both the static and dynamic problems and completely cures the half-tank-lean syndrome. Apparently the other mods do as well, but the modified uniflow is a very easy mod to do and only costs about $10.

sharkattack99

thanks i may try that mod looks like it may be easier then the mid tank mod were you have to fab and move stuff, i do have an 086 tuned pipe its a dynimite platium. but i will order the parts for that mod and work on it thanks again.

so you just drill a hole in the bottom of the tank and screw the nipple on and connect the fuel line to the t-fitting right. what about priming? can you still blow into the pressure line to prime the engine? or does the one way valve prevent that?

one more thing what size drill bit did you use the drill the hole for the nipple?

MotorBreathLT1

I did the inkpen trick on my tank, its probably 90 percent taken care of. For a free mod it works great!