Very strange fuel tank problem

[upbasher1]

Huge props to whoever can help me figure this doozy out. I have a mid tank savage and I got a really weird fuel tank problem. I first tried a hobao fuel tank: https://www.ebay.com/itm/HoBao-8707...347360&hash=item2ce32d694a:g:QEMAAOSw74RdoidT

And I cannot get the thing to run no matter what I do. Engine floods immediately as soon as you start pulling it over. Take out plug, drain excess out, reassemble, engine fires a couple times then immediately floods again. And it floods BAD. It drains the tank right into the engine, pours out the exhaust. Tried a different engine, same thing.
Took fuel tank out and held it by hand and put fuel in it, and all the fuel immediately drains right out the tank out the fuel line. All of it, right down to the bottom of the tank. :O. Without any back pressure. Cannot figure it out, never seen this before and don't know how it does it since it seems to defy basic physics. So I figured oh well Ill just try a different kind of tank, and bought this: https://www.ebay.com/itm/Hobao-1-8-...610764&hash=item1cc26281db:g:C7YAAOSwDlRcAfNv

And what do you know, it does the SAME THING. How do the tanks do this? Is there a obvious reason I'm missing as to why the fuel completely drains out of the tank without any back pressure? Its impossible to get any engine you hook them up to to run. Any ideas are appreciated

 

[Renots]

Hmmm... it sounds like it might be a carburetor issue...? Maybe?
Have you tried a different engine and carburetor setup?
Btw, I’m totally guessing here.

 

[upbasher1]

Hmmm... it sounds like it might be a carburetor issue...? Maybe?
Have you tried a different engine and carburetor setup?
Btw, I’m totally guessing here.

Yep. I have tried three different engines/carburetors. All the same problem

 

[olds97_lss]

Got a photo of your setup?

 

[upbasher1]

Sure here's some pics. The fuel just comes pouring out the fuel line and fills the engine

 

[olds97_lss]

Is that filter looking thing on the side of the tank a filter or one way check valve?

I never ran a mid tank... but it would stand to reason if the level of the fuel in the tank outlet is that much higher than the carb inlet... once a siphon starts, there's nothing really to stop it trying to get into the engine. With the engine running, it would burn what comes in, but once it dies (or while trying to start), that fuel/siphon has a path into the engine as the LSN never fully closes or the engine wouldn't run.

 

[upbasher1]

It is a filter

 

[upbasher1]

So I also have a 250cc ofna tank which I know is one of the most commonly used tanks for midtank mods. Tried that one and does the same thing also. I notice that whenever I hold the fuel line end at the same level or higher than the level of the fuel in the tank, it stops coming out.....SO okay I can live with that. But I see mid tank mods ALL OVER the place using this same tank and its way higher than the carburetor, with juist a straight line line going to the inlet. So what am I missing? How is everybody else getting these mid tanks to work without immediately flooding the engine????

 

[olds97_lss]

Just for stupid sake, what if you raise the line between the carb and tank up and ziptie it up on the roll bar so there's a dip in the line between the tank and the roll bar.

Honestly, don't know. I don't use a stock tank, but I never had a tank on any vehicle setup where the fuel flow was totally downhill from the tank, there was always a dip, then the line went back up to the carb.

 

[upbasher1]

Tried that already with no luck
I can make loops around the roll bar and it still comes out by itself

 

[upbasher1]

Still cant figure this out. Ive tried routing the fuel line every which way and it just doesnt work. Fuel will not stop coming out the fuel line. I have never seen a mid tank savage where the fuel outlet was lower than the carb....Ive got to be missing something what is it????

 

[ez2frag]

I would suggest taking the exhaust tip silicone extension off of the pipe and try. I used one and had the same problem, it was increasing the the pressure going to the tank and flooding it.. Especially if the extension has even a slightly smaller ID that the tuned pipe outlet not to mention the 45 degree bend. Put a larger diameter piece of fuel line on it straight out the bottom and worked like a champ.

 

[ELWOOD]

@upbasher1 Have you found a fix yet ???

 

[upbasher1]

@upbasher1 Have you found a fix yet ???

Well sort of. I managed to eliminate the problem but not in the way that I'd hoped. I had to crank the low speed needle ALL THE WAY IN to get it to stop flooding. Running a lrp .32 spec 4 pullstart with the stock carb. It runs and tunes just fine and actually likes the low speed needle all the way in. Its very strange but it works.

 

[ELWOOD]

Yep. I have tried three different engines/carburetors. All the same problem

Wow , with three different engines/carbs it though it would be the tank, well glad it's "working".

 

[upbasher1]

Wow , with three different engines/carbs it though it would be the tank, well glad it's "working".

Yeah same. I have done a mid tank before and got it to work just fine but idk what the deal is with this one. Have tried it with a couple different style tanks as well and same result. I'm sure I'm missing something but I cant figure it out. I doubt anybody else has had to basically eliminate their low speed needle to run a mid tank lol

 

[Seanthemechanic]

Tank is too high. Gravity! Even with the needle so lean it’s still getting plenty of volume fed to it

 

[upbasher1]

Tank is too high. Gravity! Even with the needle so lean it’s still getting plenty of volume fed to it

Yeah thats exactly it too. I've looked at all the other mid tank builds I can find and every one of them the tank is mounted in the exact same spot mine is, fuel outlet the same height relative to the carb. And none of them mention having to mess with the carb so much to make it work.