Chainsaw Gas Cap Not Venting (Explained)

If your chainsaw’s gas cap isn’t venting, it can lead to fuel flow and engine performance issues. Potential solutions include checking for a clogged vent caused by debris obstructing air entry, replacing the cap with a vented one for proper airflow, removing a malfunctioning rubber flap in some caps, and installing a separate tank vent if the cap lacks venting. Always prioritize safety, including wearing protective gear and disconnecting the spark plug before maintenance.

A chainsaw is used in different activities such as bucking, limbing, tree felling, cutting firebreaks, pruning, firewood harvesting, and wildland fire suppression.

The benefit of using a chainsaw is that it allows you to accomplish more in a shorter time.

A chainsaw is a versatile piece of equipment useful for many applications.

Chainsaw gas cap not venting

Does a chainsaw gas cap feature a vent?

Yes, there is a gas cap on the chainsaw covering the tank, and the cap is firm avoiding spilling gas while you are cutting or felling trees.

It is designed to vent the heated gases that are in excess and to maintain the pressure in the right amount.

Thus, it allows the fuel to pump into the carburetor through the fuel line.

The vent appears on the gas cap. The hole in the vent is in the cap lip. A vented gas cap allows the tank to breathe.

Your tank needs the vent to relieve the vacuum and pressure building up inside.

Gasoline expands as it warms up in volume, and on cooling down it shrinks.

How to vent a gas cap

A vent on a gas cap is necessary if you do not have a vent or the vent is not enough.

You can always drill a small hole that is not more than 1/16”, and ensure it passes through the cap edge.

It should be perpendicular to the first hole so that they match up.

It allows the vessel to vent and ensures you turn it to 90 degrees so that the gas or oil has enough breathing space.

The working of the vented gas cap

The design of the vented gas cap is the small amounts of air filling into the gas tank line.

The gas cap vent gets to release as one-way when the pressure activates inside.

With the pressure reaching a certain point, the valve opens by a small amount, relieving the pressure.

Thus, the pressure is formed on the tank outside, while the vacuum is formed due to the fuel displacement inside.

Having the vented gas cap helps as the pressure within the line equalizes by breathing through the vent.

It gets to balance the pressure with the surrounding atmosphere, where the air goes in, but the gas cap does not allow fumes outside, ensuring any environmental concerns.

Inner Parts

The gas cap vented features a chamber beneath the cap going into the fuel line.

With the cap screws being shut, the chamber gets closed within the fuel intake tube that runs to the tank.

On the chamber each side is the small openings, allowing air to enter.

Thus, a pressure valve is created in the chamber, and as the tank level decreases, the air is allowed inside to eliminate any vacuum forming possibility.

The fuel tank receives a lot of pressure from the fuel pump, and it expands and evaporates naturally.

Therefore, a lot of pressure is created within the fuel system.

Another pressure is taken care of by the fuel pump mechanism operation, as there is a need for the vented gas cap to be a single-way flap, and it holds the evaporated gas fumes within.

How to fix a ‘fixed’ vented chainsaw gas cap

Getting a new cap or some used cap is impossible.

However, it is possible to fix a ‘fixed’ vented chainsaw gas cap using a duckbill rubber vent.

You have to fire it and spay gas, the vent will open into the tank and allow the rubber part to intake the air, and keep a check to not let the gas leak out. 

Replacing a gas cap of the chainsaw

There are times when the gas caps give away.

The manufacturers design the caps such that clicking once allows them to tighten correctly.

You can understand it has fit properly.

However, a damaged gas cap does not tighten, and you do not listen to the clicking sound that you get to listen to when the gas cap fits perfectly.

Occasionally, the gas cap pops after tightening.

These are the indications for you to understand the gas cap needs replacement.

Replacing a gas cap means it should move freely on the thread. Remove it by lifting away from the fuel tank neck opening.

However, keep the old cap unless you are sure the replacement cap fits accurately and is installed properly.

On lifting away the old gas cap, you may place the new gas cap.

Leaking gas cap on the chainsaw

The chainsaw gas cap keeps the tank safe, and the gas does not spill out during activity.

The gas cap design is such that the vent excess heated gas keeps the pressure in the right amount.

It allows the pumping of the fuel through the fuel line. The gaps damage or become dirty after stopping refueling.

For leaking gas, you may:

Look for damage signs

Unscrew from the gas tank the gas cap, and inspect it for cracks or hole signs.

If there are cracks, you may replace them. On the cap’s inner side, you may inspect the rubber washer.

It offers an airtight seal and ensures the rubber washer is in place as mostly it is lost in the process of refueling.

If the rubber washer is not in place, you have no choice, but to replace it.

Gas cap cleaning

The gas cap becomes dirty and requires cleaning. You may pour clean gasoline a capful onto the gas cap.

Clean the gas cap using a wire brush and wipe with a rag dry. Inspect the cap for cracking or breaking signs.

On noticing damages, there is a need for the replacement of a gas cap.

Check the vent hole

Getting rid of gas heat through the vent hole helps keep the gas cap safe.

Anyhow, when there is leaking gas, it is best to inspect the vent hole on the gas cap by flipping the gas cap upside-down.

If you find the vent hole in broken condition or is clogged or ripped open, the gas will leak to other areas.

You may replace the cap and ensure to see if it is leaking still.

Final Thought

The gas cap on the chainsaw is important and so is the vent on the gas cap.

However, if the gas is leaking, by any chance, it is a must to identify the leakage and fix it.

You cannot keep a broken or warped gad cap.

It gets warped due to overheating, and if so you must consider replacing the gas cap to stop leakage.

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