Very strange fuel tank problem

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Old 11-03-2019, 02:15 PM
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Default Very strange fuel tank problem

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 from a hyper 7 TQ.
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 one from a hyper ss.
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
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Old 11-03-2019, 04:19 PM
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The one you bought was it new or used? I had an issue like that once. Ended up being a crack in the tank. Just for giggles. Take take off and pressure test it under water.
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Old 11-03-2019, 04:22 PM
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Why are you not using a Savage tank? Is the tank you're using mounted higher that the carb? If so, it can siphon right into the carb.
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Old 11-03-2019, 04:40 PM
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Yeah make sure the tank outlet is lower than where it enters the carb.
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Old 11-03-2019, 05:09 PM
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Originally Posted by Lovestricken View Post
The one you bought was it new or used? I had an issue like that once. Ended up being a crack in the tank. Just for giggles. Take take off and pressure test it under water.
It is a mid tanked savage. I have the tank mounted where the radio box comes stock. Throttle servo located next to engine. Yes the tank outlet is higher than the carb. But I have the fuel line go up and over the roll bar and it still does it. Even with gravity working against it. On both tanks. Also on these tanks the fuel outlet is on the TOP of the tank, not the bottom, so shouldnt the fuel stay in the tank unless theres pressure coming in??? I know for a fact on the stock savage tank the fuel does not come out of the tank unless you have pressure, even when the tank is full. And yes these tanks I am trying are both brand new
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Old 11-03-2019, 05:36 PM
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Do the tanks have clunks that are resting at the bottom of the tank? I forgot about the clunk.
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Old 11-03-2019, 07:45 PM
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Originally Posted by frewster View Post
Do the tanks have clunks that are resting at the bottom of the tank? I forgot about the clunk.
They do not. They are just the basic pickups built into the tank
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Old 11-04-2019, 06:44 AM
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Originally Posted by upbasher1 View Post
It is a mid tanked savage. I have the tank mounted where the radio box comes stock. Throttle servo located next to engine. Yes the tank outlet is higher than the carb. But I have the fuel line go up and over the roll bar and it still does it. Even with gravity working against it. On both tanks. Also on these tanks the fuel outlet is on the TOP of the tank, not the bottom, so shouldnt the fuel stay in the tank unless theres pressure coming in??? I know for a fact on the stock savage tank the fuel does not come out of the tank unless you have pressure, even when the tank is full. And yes these tanks I am trying are both brand new
Fuel outlet on the top does not sound right to me. Try swapping the fuel and pressure lines and see what happens. The pressure line should be attached at the fuel cap lid.
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Old 11-04-2019, 07:50 AM
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Originally Posted by jmackani View Post
Fuel outlet on the top does not sound right to me. Try swapping the fuel and pressure lines and see what happens. The pressure line should be attached at the fuel cap lid.
The pressure line is on the lid on both of them. They are connected correctly
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Old 11-04-2019, 08:43 AM
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It doesn't matter if you run fuel line to the moon and back (ok I'm exaggerating that wouldn't work) what matters is the fuel level relative to the carb inlet. If the fuel level is higher than the carb inlet, fuel will siphon out of the tank into the carb.
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Old 11-04-2019, 08:55 AM
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Originally Posted by wingracer View Post
It doesn't matter if you run fuel line to the moon and back (ok I'm exaggerating that wouldn't work) what matters is the fuel level relative to the carb inlet. If the fuel level is higher than the carb inlet, fuel will siphon out of the tank into the carb.
So what do I do then? How do I get this to work? How do other people get it to work? I know I've built a mid tank savage before with this same setup and never had this problem....There has to be something Im just drawing a blank on....anyway heres some pics of what Im working with

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Old 11-04-2019, 05:57 PM
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Looking at that high speed needle is the first thing i think you need to try. Lean out the engine some. Changing tanks and stuff can affect the tune. Leaning that hsn will fix the issue that is like the master flow valve in reality for the engine. Close it far enough and it will not let any fuel into the engine.
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Old 11-05-2019, 12:17 AM
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That thing in the pressure linr, is that just a filter or is it a oneway valve?
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Old 11-08-2019, 08:38 PM
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Nothing on the pressure side. Caught me off guard as well lol.
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Old 11-09-2019, 11:43 AM
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It is a brand new engine at stock needle settings. I figured leaning out the hsn before even breaking it in would be a bad idea.....and yeah that is a filter and its on the fuel line, nothing on the pressure line
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