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Old 06-23-2009, 03:59 AM   #1
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Default Fuel tube length!!!!!!!

Any one know the proper length for fuel tube. And how will short / long tube affect your tune??!??
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Last edited by JPierson; 06-23-2009 at 09:12 AM.
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Old 06-23-2009, 04:33 AM   #2
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I usually run just enough to put me close to the legal fuel capacity. If you don't have a way to check capacity or are not worried about it, I would just run the minimum amount it takes to get from the carb to the tank. The more tubing you run the leaner the motor gets. Its like a water hose, the longer the hose, the less pressure you get at the end. Eventually, if its too long, you won't be able to tune it.
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Old 06-23-2009, 07:51 AM   #3
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True.
Tried to use lengthened fuel side tube (to carb)n as a friend suggested me that it would:
- longer time before flameout when upside down (only partially true)
- better idle (not at all)
- more consistent fuel flow (nope)
- more available fuel makes more runtime (yes, but not that effective)
What happened was:
- when upside down, the buggy has more time before runs out of fuel, but counter-acted by the poor idle quality in the first place)
- fuel mixture get lean and rich (fluctuates) greatly during run

So next week i would run my previous setup, which is the shortest path from tank to carb.
Got good runtime already from good balance of track design, pipe selection, gearing, fuel used, venturi size, glow plug, and (very important) how you oil your air filter. Plus, driver's driving style

Fiddle right, and everything is gonna be alright
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Old 06-23-2009, 08:06 AM   #4
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On a side note:

Make sure that the tube doesn't bend or curve at extreme angles, especially going upwards, as this would increase the possibility of air bubbles inside the tube.
Makes suddenly lean 'power boost' (usually after high speed turn on half throttle or hard deceleration) and runs hotter 'with no reason'.

To give an opinion about length, mine generally measures 10-15 cm take or give some milimeters.
Happy tuning
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Old 06-23-2009, 08:28 AM   #5
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just run the stock set up - I have never had a problem like that - no problem tuning - I think when people say oh its better whe you flip.

First of all no its not - most tanks for racing have stones in them to moves with the tank so it will still get fuel to the carb - period, just keep you engine clear so you wont flood and flame out. I rev the sh!t out of mine until the marshall gets there.

Second when your racing - YOU HAVE MARSHALLS - so you wont be on your lid long.

Its all about drive skills - stop trying to cheat the system and sneak fuel everywhere - this is suppose to be a FUN hobby. I recently seen some one banned froma track becasue he took the block out of his tank for more fuel. And he was a good driver and had a 1 lap lead - he still pitted with the crowd

That is bad sportmanship and sucks.

Just run your specs learn to drive and have fun. This cost to much money to be worring about trying to get 30 more seconds out of your fuel.


Not point fingers at any one person just stating a opinion of my own so dont have a cow dudes
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Old 06-23-2009, 08:53 AM   #6
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Originally Posted by token View Post
just run the stock set up - I have never had a problem like that - no problem tuning - I think when people say oh its better whe you flip.

First of all no its not - most tanks for racing have stones in them to moves with the tank so it will still get fuel to the carb - period, just keep you engine clear so you wont flood and flame out. I rev the sh!t out of mine until the marshall gets there.
The Losi buggy is the only one that has a "clunk" in the tank. Every other car that I know of has a fixed fuel pick-up in the tank so the engine will not run indefinitely when the car is upside down.

Also, I don't recommend "revving the sh!t" out of your engine while waiting to be marshaled. It just means that most people will run out of fuel faster when they're upside down. If you need to, then maybe it's time to re-tune the engine. The best thing you can do is let it sit there and idle. It's the classic Mexican stand-off. The marshal won't get near your car because you're "revving the sh!t out of it" and you're "revving the sh!t out of it" because the marshal hasn't touched your car yet.
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Old 06-23-2009, 09:10 AM   #7
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The d8 has a clunk style tank stock. Thanks for all the posts good info guys!
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Old 06-23-2009, 09:19 AM   #8
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Originally Posted by SteveP View Post
The Losi buggy is the only one that has a "clunk" in the tank. Every other car that I know of has a fixed fuel pick-up in the tank so the engine will not run indefinitely when the car is upside down.

Also, I don't recommend "revving the sh!t" out of your engine while waiting to be marshaled. It just means that most people will run out of fuel faster when they're upside down. If you need to, then maybe it's time to re-tune the engine. The best thing you can do is let it sit there and idle. It's the classic Mexican stand-off. The marshal won't get near your car because you're "revving the sh!t out of it" and you're "revving the sh!t out of it" because the marshal hasn't touched your car yet.
I am not a newbie here - I get 9 mins a tank Revvin when I flip, I have NEVER in my 20+ years of racing had a marshal not flip my car over, once they get there I brake and they flip, and in my many of years in the hobby I have never seen anyone just sit there and idle - like at the start of a race everyone on the drivers stand revs there engine to keep them clear - thats y down and quite is so fast, so fuel dont build up in engine. My tune is great, and I'm not most people , nor am I the only one that does it. Oh I did not reccommend - I stated what I do. If my engine blow screw it - it blows. You can take it easy on you engine but for $500 I am going to push it as hard as it can go
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Old 06-23-2009, 09:23 AM   #9
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oh forgot


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Old 06-25-2009, 11:38 AM   #10
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if you are going racing you mast have 125cc with fuel with all the fuel line................
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Old 06-25-2009, 11:42 AM   #11
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150 in truggy
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Old 06-25-2009, 12:09 PM   #12
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Just install a second tank, paint it black and no one will know hahah
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Old 06-25-2009, 07:24 PM   #13
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Originally Posted by Miniracer23 View Post
The more tubing you run the leaner the motor gets. Its like a water hose, the longer the hose, the less pressure you get at the end. Eventually, if its too long, you won't be able to tune it.
Actually, that's not true.

Liquids are incompressible so the pressure at the entrance is the same as the pressure at the exit, assuming your fuel tubing is the same size at the entrance and the exit of the tube. If the size of the tubing changes it changes the pressure but it also changes the speed of the delivery. Think of a nozzle... smaller hole and it speed up the water exiting the hose. The same amount of water will come out at the same rate, it's just faster.

I run two empty fuel filters on my truck so I can run shorter fuel tubing just because I like how it looks better and it's easier to work on the truck.

In my case it would come out of the tank, hit the filter and slow down, speed up again on the way to the next filter, slow down again and then speed up to the original speed and pressure to enter the carb.

If you change the length of the fuel tube going from your pipe to your tank, that's a different story.

That tube is moving a gas (exhaust) wich is compressible. If you're changing the pressure with a larger volume of gas it takes longer for the pressure to rise.. so with a longer tank pressure line it will take longer for the tank to pressurize and you may run lean when you blip the throttle or punch the gas.

The opposite is true with too short of a fuel line, it will cause the truck to run rich for a moment when blipping the throttle or punching the gas because the tank pressurizes instantly. The length of the tank pressure line isn't hugely noticable but it is moreso depending on the engine and pipe.

I hope that made sense, it did when I typed it, haha.
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Old 06-25-2009, 08:12 PM   #14
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yeup it did great info thanks!
im thinking about getting a fuel filter for my buggy now. so would it be ok to just cut the line as is and install the fuel filter? or will i need to shorten the line any?
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Old 06-25-2009, 08:24 PM   #15
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Acceptable line length is different for different cars,actually the tanks. Some tanks have a larger I.D. of the pipe inside the tank & different pressure baffles in the lid. Extreame example is my mbx5 going to my 808. I swaped the motor,clutch,pipe,& both lines directly off my mugen with extreamly long fuel line straight into my 808 with out disconecting anything bit the 2 tank connection & changing CB. What I had was a perfectly tuned motor in 1 car & 15 min later on start up I had a 15,000 rpm idle with the only difference in fuel system being the tank. IDK if it was the baffle or pickup I.D. but the tank made a difference in what was acceptable line length. Short of it is just because your buddy runs a long enough fuel line that he can flip,walk off the stand,across the track & start driving from down there without walking back to the pits for a restart dont mean your car can unless of course you both drive the same car.Best advice is dont crash on practice/play days.
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