Gas Cap Seal | Honda CT90 / Trail 90
A cracked gas cap seal is the most overlooked fuel leak on a Trail 90. The original rubber — and the even-older cork — seals shrink and harden with age, and fuel starts weeping out from under the cap. This is the OEM-spec replacement seal that drops into your existing CT90 or CT200 gas cap.
Why You Need This
The seal sits inside the twist-on gas cap, pressed flat under the locking tabs. After decades of fuel and heat the rubber goes brittle and the old cork versions crumble — either way, the cap stops sealing and you get the smell of gas and a wet ring around the filler neck. A fresh seal restores a clean seal between the cap and the tank.
This seal fits every CT90 and CT200 gas cap, including the cap on the auxiliary fuel tank Honda added at the K4 — the blank cap on the main tank and the "GAS"-stamped cap on the spare tank both take the same seal.
Specifications
| Spec | Detail |
|---|
| OEM Part Numbers | 17631-096-702, 17631-001-000, 17631-096-701, 17631-096-700 |
| Fits Models | CT90 / Trail 90 K0–K9 and 1979 (1966–1979), CT200 |
| Material | Rubber |
| Sold As | Sold individually |
Note: Fits all CT90 and CT200 gas caps, including the auxiliary fuel tank fitted to the K4 and later.
Installation
Difficulty: Beginner
Tools needed: Small flathead screwdriver, wire brush
- Pop the old seal out of the cap. Old rubber goes brittle and old cork tends to break off in chunks — pick out every last bit so the new seal can seat flat.
- Clean any rust or corrosion off the inside of the cap with a wire brush so the seal has a clean surface to press against.
- Stretch the new seal over the cap and work it into place, thin side facing up toward the inside of the cap.
- Make sure it's seated flat and fully under the cap's locking tabs before you twist the cap back on. Take your time — it goes in tighter than you'd expect.
Our video covers gas cap seal replacement as one of five often-missed maintenance jobs on vintage Hondas — cleaning the cap and stretching the new seal on without tearing it.
Frequently Asked Questions
Does this fit the spare / auxiliary fuel tank?
Yes. The same seal fits the main-tank cap and the auxiliary "GAS" tank cap Honda added at the CT90 K4. One seal covers every CT90 and CT200 gas cap.
My tank still weeps a little when it's full and on the kickstand — is the seal bad?
Not necessarily. The cap is a fuel seal, not a pressure-tight cap. A brimming tank leaned over on the side stand can push a little fuel up past even a good seal. Fill to just below the neck and the weeping usually stops. If fuel runs out steadily with the bike upright, re-check that the seal is seated flat under the tabs.
What's the seal made of?
Rubber — the OEM-spec replacement for the original rubber and cork seals, which dry out and crack with age.
How do I know my gas cap seal is bad?
The smell of gas, a wet ring around the filler neck, or fuel weeping onto the top of the tank are the usual signs. Pop the cap and look at the seal — if it's hard, cracked, flattened, or crumbling, it's done.
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Last updated: June 2026
