Setting up a gas tank

Tutorials > Setting up a gas tank


Plan Components Bottle Lines Install Connect Three line system

An airplane with a two-stroke gasoline engine requires a fuel tank, a way to get the fuel to the carburetor, a method of filling the tank and a way to vent it. There are different ways to do it; this tutorial describes an approach has worked well for me - a two line system based on a Fiji water bottle.

Photos were taken from two different setups so two different bottle sizes will appear - 500 mL for a 50cc engine, and 360 mL for a 20cc engine.


Plan the system

It's essential to plan the system beforehand to determine what parts and supplies you'll need and the placement of the tanks and lines.

Two-line gas engine setup

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Here's a look at a fuel system ready for installation.

Fuel tank with all lines connected - vent, fill and supply

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Assemble the components

Time to get all the stuff together!

Everything starts with the bottle. Fiji bottles are light, strong and square and are available in varying sizes - 360 mL, 500 mL and 1L.

Fiji bottle mockup

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This cap from PSP Manufacturing is a perfect fit for Fiji bottles and features outer and inner barbs.

New parts - Fiji water bottle cap

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The single barb vent, also from PSP Manufacturing, is ideal for connecting the vent line.

New parts - Single barb vent

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My choice of pickup is the Walbro felt clunk.

New parts - Walbro felt clunk

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For extra insurance I put a fuel filter in between the tee and the carburetor.

New inline fuel filter

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This fuel dot is made by McFueler.

McFueler after polishing

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I use this part from Hangar 9 as a vent line fitting.

New vent line fitting

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A package of fuel tees - only one is required.

New parts - Fuel tees

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Tygon tubing for everything outside of the tank.

New parts - 5' Tygon tubing

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Viton tubing for the in-tank line.

New parts - 1' Viton tubing

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An assortment of zip ties; I use a small size.

Assorted zip ties

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The tank should sit on foam.

Foam in place

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Velcro is a good way to secure the tank.

Velcro for the fuel tank

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Prepare the bottle

Start by testing the cap - I came across a bottle that the cap would not thread onto.

Fiji bottle with PSP cap

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Drill the vent hole - make sure the location suits the planned installation. I use a brad point drill bit because the spurs scribe a nice clean hole; I turn it with my fingers for better control.

Drilling the vent hole

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A nice clean hole.

There's the hole

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Time to install the barb. Start by dropping it into the bottle.

Vent fitting inside the tank

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A piece of wire helps guide it into position.

A piece of wire helps guide it in

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There's an internal keyway for a hex driver - insert that...

There is a central keyway for a hex driver

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...then hold onto it while tightening the nut with a wrench.

Hold with the hex driver, tighten with the wrench

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Barb installed.

Vent fitting installed

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Configure the lines

Take a minute to determine the required length of the lines for the clunk, carb, vent and fill. Be generous - better too long than too short!

Here's a carburetor line.

Engine supply line marked for cutting

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And here a vent line is marked.

Marking the vent line length

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Attach the felt clunk to the Viton line and inner cap barb.

Felt clunk

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Install the cap and ensure that the clunk reaches as far as possible without catching on the inside of the bottle.

Clunk clears bottom of tank

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Attach the vent line to the barb.

Vent line on the fuel tank barb

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Build the supply ine to the carb, incorporating the tee for the fill line and the filter. Note the missing zip tie on the tee side of the filter - that was installed after the photo was taken.

Supply line complete

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The fuel system, ready to install.

Fuel tank with all lines connected - vent, fill and supply

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Install the tank

Installing the tank is a quick job. Be sure to route the vent line down and along the side of the tank - this prevents gas from leaking out of the vent line during flight.

Vent line wrapped

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Connect the system

The final piece of the puzzle - making the connections.

Connect the carburetor supply line.

Attaching the fuel line

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Don't forget the zip tie!

Fuel line secured to carb

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Route the vent line and connect it to the fitting.

Vent line path

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Connect the fill line to the tee and route it out of the fuel dot housing.

Filler line out of the port'

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Connect the fuel dot.

Fuel dot installed - out

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Installation complete.

Three line system

Since I started flying gas airplanes in 2012 I've used a two-line gas system. I use a filter in the gas can, a felt fuel clunk in the gas tank, and an in-line filter in the supply line to the carburetor. It was recently pointed out to me that this might not be the best approach; consider the following diagram:

Two line gas setup - flaws

The blue arrows indicate five additional points for potential air leaks. A three line system requires neither the T-fitting nor the inline filter (pumping gas into the tank through the felt clunk negates its effect as a filter, which is why I add a separate one in the supply line). I've switched to 3-line setups.

3-line gas tank

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