Are gas caps universal?

No, there are many different kinds of gas caps and you need to know what kind you have in order to replace it. Older model motorcycles have bayonet / cam-style gas caps (sometimes referred to as ¼ turn gas caps) that engage using a notch and a twist. Other gas caps are threaded and they screw into the tank. Not all manufacturers use the same threads so you need to find a gas cap that is made for your particular bike. It’s also important to note that some gas caps have vents that help eliminate vapor lock which can stop fuel from flowing properly.

Can a bad gas cap cause idle problems?

Yes. Most gas caps have vents. These one-way valves help allow air in so the gas flows out of the gas tank petcock. Just like the vent on the gas can you use to fill your lawn mower. If the vent is closed the gas comes out of the can very slowly. If you open the vent, the gas will flow out freely. If your vent is stuck or clogged then the gas will not flow out properly, which can cause a situation where your bike needs more fuel to run and simply will not due to lack of fuel flow. If the vent is completely stuck or clogged then your bike may idle for a while and then die. An easy way to test if this is your problem is to simply remove your gas cap and check if the motorcycle keeps running. An insufficiently sized vent or partially clogged gas cap vent can cause a bit of fuel starvation when riding at high speeds for extended periods, causing your bike to run lean, and not generate as much power.

What happens if you lose your motorcycle gas cap? Can you ride without one?

Yes, you can ride without your gas cap, but it definitely is a messy endeavor. Depending on your fuel level, gas will splash out of your motorcycle gas tank when you hit a bump. This combined with the wind will translate to you wearing most of the fuel that comes out of the tank. We highly advise against smoking if you have to travel without a gas cap for obvious reasons. When in a pinch, stuff a rag in the filler hole of your gas tank until you can get off the road and locate a new (or retrieve your lost) gas cap.

Why people often replace factory gas caps with after market ones?

People replace factory gas caps for a few reasons. Some factory gas caps rattle and this can be quite annoying, so people replace them. Another reason is because of poor design. A lot of riders wear gloves when they ride. Trying to open a factory gas cap with a smooth surface does not allow for much grip. Spinner gas caps and other designs are easier to grab with gloves on. Another reason is for security. Some people want to have a lock on their gas cap. This can help eliminate the risk of people stealing your fuel, or putting something into your tank. The most common reason is simply aesthetics. Pop-up gas caps are popular because they sit flush on the tank, and some people think they look cool. Sometimes a rider simply wants a different material or finish gas cap, such as a black or brass gas cap for Harleys. Changing out a stock gas cap for a custom one is a very quick and inexpensive process, and can add some personal style to a motorcycle.

Harley-Davidson Sportster Mooneyes Motorcycle Gas Caps

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