Flip-Up Gas Cap Seal | Honda Twins and Inline Fours
The rubber seal inside your flip-up gas cap shrinks, cracks, and goes brittle over time — even when it still looks OK from the outside. Once it fails, fuel leaks out around the cap and onto your paint. This OEM-spec replacement seal fits all 1970s-era Honda twins and inline fours equipped with flip-up gas caps.
Why You Need This
A degraded gas cap seal lets fuel seep past the cap every time you ride, staining your paint and wasting gas. The rubber hardens with age and loses its ability to conform to the filler neck opening. Even seals that look fine on the surface can be completely brittle underneath — the moment you try to remove one, it crumbles apart.
This replacement seal is made to OEM specifications and restores a tight, leak-free fit to your flip-up gas cap.
Specifications
| Spec | Detail |
|---|
| Replaces OEM Part Numbers | 17534-323-300, 17525-300-000 |
| Fits Models | CB200 (1973–1976), CL200 (1974), CB350 K3–K5 (1971–1973), CL350 K3–K5 (1971–1973), SL350 K2 (1972–1973), CB350F (1972–1974), CB360 (1974–1976), CL360 K0–K1 (1974–1975), CB450 K3–K7 (1970–1974), CL450 K3–K6 (1970–1974), CB500T (1975–1976), CB500 K0–K2 (1971–1973), CB550 K0–K2 (1974–1976), CB550F (1975–1976), CB750 K2–K5 (1972–1975), CB750F0–F1 (1975–1976), CB750A (1976) |
| Sold As | Individual seal |
| Material | Rubber |
Note: This gas cap seal only fits bikes equipped with flip-up gas caps and those with recessed fuel caps covered by fuel doors like the later CB750s. It does NOT fit early bikes with screw-in gas caps or CB175s. Specifically, the CB175, CL175, CB350 K0–K2, CL350 K0–K2, SL350 K0–K1, and CB450 K0–K2 all used screw-in caps and require a different seal.
Installation
Difficulty: Beginner
- Pry out or peel off the old seal from the stopper inside your gas cap. The old rubber may look intact but will likely crumble once you start removing it.
- Clean any corrosion or rust off the gas cap stopper with a wire brush.
- Carefully stretch the new seal over the circumference of the stopper. The seal has a thick side and a thin side — install it so the thin side faces up toward the inside of the cap. When the cap is closed, the thicker side of the ring should face the opening of the gas tank.
- Work the seal evenly around the full circumference. This takes more time than you would expect to get it seated evenly.
Our 5 Small Maintenance Jobs Often Missed video covers gas cap seal replacement along with other common maintenance items.
Frequently Asked Questions
Does this fit my CB175 or early CB350?
No. The CB175, CL175, and early CB350 K0–K2 / CL350 K0–K2 / CB450 K0–K2 all used screw-in gas caps, not flip-up caps. This seal is only for the flip-up style. If your bike has a twist-on cap, check our Chrome Twist-On Gas Cap instead.
How do I know which side faces up?
The seal has a thin side and a thick side. Install it with the thin side facing up toward the inside of the gas cap. When the cap is closed, the thicker portion faces the tank opening to create a tight seal against the filler neck.
Will this fix fuel leaking from my gas cap?
In most cases, yes. A cracked or hardened seal is the most common cause of fuel leaking around the gas cap on these bikes. If the seal is new and you still have a leak, check that your gas cap body itself is not bent or damaged, and that the cap latch mechanism is holding the cap down firmly against the tank.
Does this fit the CB750?
Yes — it fits the CB750 K2–K5 (1972–1975), CB750F Super Sport (1975–1976), and CB750A Hondamatic (1976). These models all use the same flip-up style gas cap. Earlier CB750 K0–K1 models used a different cap design.
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Last updated: March 2026
