What Is Polyurethane Fuel Line? (ID & OD Sizing)

Polyurethane fuel line is flexible polymer tubing used to carry fuel only when its maker rates that exact product for the fuel and service conditions. There is no single OEM, corporate lineage, universal size, or fuel-compatibility rating for “polyurethane” tubing. Choose by inside diameter (ID), outside diameter (OD), circuit, and immersion rating—not by material name alone.

Why ID and OD both matter

Fuel-line sizing describes two different measurements: ID controls the opening through the tube, while OD controls how much space the tube takes up outside. Both affect fit, but neither measurement alone proves that a line is safe for a particular fuel.

There is no one manufacturer or corporate origin behind all polyurethane fuel tubing. “Polyurethane” names a broad material category, not a specific fuel-line product or a shared engineering rating. Tubing makers may offer products with different formulas and uses, so check the exact product’s specifications.

The machine maker determines what its fuel circuits require. A fuel-feed line, return line, vent line, and primer line can connect to different parts and perform different jobs. A tube that fits one connection may still be wrong for another circuit or for its exposure to fuel.

Fuel-line dimensions and specification matrix

This table defines the measurements used to compare tubing and shows one example dimension only; it does not recommend a size for any particular machine. Use the equipment manual or parts listing to confirm the required material, dimensions, and fuel service.

The example row means tubing with a 1/8-inch ID and a 3/16-inch OD has a 1/32-inch wall. It is a math example, not a fit recommendation. Measure the old line and the machine’s connection points, then verify the required specifications before buying a replacement.

Identify the Fuel Circuit and Prepare the Equipment Safely

A fuel circuit is the path that a line serves, such as fuel feed, return, vent, or primer flow. Identifying that path before removal helps prevent a replacement from being fitted to the wrong connection or routed incorrectly.

Work outdoors or in an area with effective ventilation. Let the engine cool, switch the ignition off, and keep fuel away from flames, sparks, and hot surfaces. Before removing anything, take a clear photo of the line routing and note which connection each end serves.

Check the manual, parts diagram, or equipment maker’s parts listing. Look for the stated line material and size, and check whether the line sits inside the tank. If the documents do not make the requirements clear, ask the equipment maker or an authorized service source rather than guessing from appearance.

• Identify each line as feed, return, vent, or primer where the machine’s parts information allows.
• Note which line passes through a tank opening and which stays outside the tank.
• Do not treat lines as interchangeable just because they look alike or fit the same-size opening.

Measure ID and OD and Select Fuel-Compatible Tubing

ID is the inner width of a tube, and OD is its full outer width; together, they describe fit at the connection and through any opening or grommet. Measure both, then confirm the machine’s specified size and the tubing maker’s approval for the actual fuel exposure.

Match dimensions to the connection

A line’s ID must suit the nipple or barb it connects to. Its OD must suit the grommet, tank port, clamp, or available routing space. A line can fit over a barb but still be too large outside to pass through a port, or too loose inside to stay seated as intended.

Measure the old tube before it is badly damaged, if possible. A swollen, flattened, cracked, or hardened line may no longer show its original size. Compare the measurement with machine documentation and the tubing product’s listed dimensions. Do not choose tubing by OD alone.

Wall thickness helps explain why two tubes with the same ID may not fit the same opening. Calculate it as (OD − ID) ÷ 2. Use the result as a comparison aid, not as a substitute for the equipment maker’s specified dimensions.

Verify the fuel and immersion rating

Polyurethane by itself does not prove that tubing can carry gasoline, an ethanol blend, or any other fuel. Select a product whose manufacturer explicitly identifies the fuel exposure and application it supports. If the product information is unclear, do not assume compatibility.

An in-tank pickup line needs tubing specifically approved by the equipment or tubing maker for submerged fuel service. Ordinary tubing intended for an external route may soften, swell, or fail when immersed. A fuel-compatible external line is not automatically suitable inside the tank.

Check the line’s intended circuit as well as its material. A vent or primer line may have different dimensions or construction needs from a pickup line. Do not infer fuel-oil ratios, engine speed, chain pitch, or other machine settings from tubing dimensions; those specifications come from the machine maker.

Install, Route, and Leak-Test the Line

Installation means replacing each identified line with the specified fuel-compatible tubing while preserving its original route and connection points. Correct routing and a leak check help reveal a poor fit or material problem before the equipment is used.

Drain fuel safely and follow the machine maker’s service instructions. Remove the old line without damaging the tank opening, grommet, or connection. Cut replacement tubing squarely if cutting is needed, and route it as the original line ran.

Keep the replacement away from kinks, pinching, sharp edges, hot parts, and moving parts. Seat it fully on its connections and refit the specified clamps or grommets. Do not stretch, glue, or heat the tubing unless the equipment maker directs you to do so.

Refill with the specified fuel and prime as directed by the machine maker. Before starting the engine, inspect the tank and every connection for wetness or seepage. If you see a leak or smell fuel, stop and correct the material or fit; do not run the engine while fuel is leaking.

Inspect for Fuel Damage and Maintain the Replacement Line

Fuel damage is a change in the tubing’s condition or performance, such as softening, swelling, cracking, or poor fuel delivery. Regular visual checks can help catch a bad material match or connection before the line fails in service.

Inspect the line where it enters the tank and where it joins a barb or fitting. Look for loose ends, cracks, flat spots, kinks, and signs of fuel wetness. A change in feel or shape can also indicate that the tubing is not suited to its exposure.

If an in-tank pickup line softens, swells, collapses, or detaches, fuel delivery may stop or become unreliable. On a running two-stroke engine, fuel starvation can create a lean condition and cause severe piston or cylinder damage. Shut the engine down immediately if fuel flow is suspect, then confirm that the replacement is approved for submerged service.

Field checks: three common sizing problems

These examples show how to reason through fit and compatibility without assuming a universal size.

• The line fits the barb but will not pass through the tank grommet. The ID may suit the connection, while the OD is too large for the opening. Check the specified OD and grommet size rather than forcing or stretching the tube.
• A replacement line looks correct but softens inside the tank. Appearance and initial fit do not establish immersion suitability. Stop using the machine and replace the line with a product explicitly approved for submerged fuel service.
• The engine has poor fuel delivery after a line change. Check for a kink, pinch, loose connection, or wrong circuit routing, then verify material and dimensions against the machine information. If a two-stroke engine may be starved of fuel, shut it down instead of continuing to test it.

Avoid fitment and part-identification traps

A parts listing for the exact machine model is a stronger starting point than a general online size chart. Model variations can affect parts, so verify the equipment’s model and any serial-number guidance in its parts information. There is no universal serial-number break for polyurethane tubing.

Compare the replacement’s labeled dimensions and fuel-use claims with the documented requirement. A product described only as “polyurethane tubing” does not establish gasoline, ethanol-blend, or submerged-fuel approval. If the product label or maker’s documentation does not answer those questions, choose a verified part instead.

Actionable sizing checklist

Use this checklist to confirm the replacement before returning the machine to service.

• Identify whether the line is feed, return, vent, or primer.
• Confirm whether it runs inside the tank or outside it.
• Check the machine manual or parts listing for the required material and size.
• Measure ID and OD, and compare both with the connections and openings.
• Verify the tubing maker’s stated fuel compatibility and submerged-service approval when needed.
• Route the line as specified, refit the correct clamps or grommets, and inspect for leaks before starting.

Frequently asked questions

What does ID mean on fuel tubing?

ID means the inside diameter of the tubing. It describes the opening through which fuel passes and helps match the line to a barb or nipple. It does not confirm fuel compatibility.

What does OD mean on fuel tubing?

OD means the tubing’s outside diameter. It matters when the line must pass through a grommet, tank port, clamp, or tight routing space. Check it alongside ID, not instead of ID.

How do I calculate fuel-line wall thickness?

Subtract ID from OD, then divide the result by two. For example, a 3/16-inch OD line with a 1/8-inch ID has a 1/32-inch wall. This calculation describes the tube; it does not show whether it fits a machine.

Is polyurethane fuel line safe for gasoline?

Polyurethane tubing is suitable for gasoline only if its maker rates that exact product for the fuel and application. The material name alone does not prove gasoline or ethanol-blend compatibility. Check the tubing maker’s product information.

Can polyurethane tubing go inside a fuel tank?

It can go inside a tank only when the equipment or tubing maker approves it for submerged fuel service. External fuel tubing may soften, swell, or fail when immersed. Verify the rating before using it as a pickup line.

Can I choose fuel line by OD alone?

No, fuel line must be checked by both ID and OD. ID affects fit at the connection, while OD affects openings and routing clearance. The line must also match the required fuel exposure and circuit.

What if the old fuel line is swollen or cracked?

Do not use a damaged line as the only guide to replacement size. Check the machine’s specified dimensions and compare them with the fittings and tubing information. Replace it with material approved for that circuit and fuel exposure.

Can I stretch tubing to make it fit?

Do not stretch the tubing unless the equipment maker specifically directs you to. A line that must be forced may have the wrong dimensions, and stretching does not establish fuel compatibility. Use the specified size and fitting method.

What should I do if a new line leaks?

Stop and correct the leak before starting or running the engine. Check that the line has the right dimensions, is fully seated, and uses the required clamps or grommets. Replace tubing that is incompatible, damaged, or incorrectly fitted.

(This article was written by one of our staff writers, Evan Bradley. Visit our Meet the Team page.)