Replacement Carburetor & Main Jet Kit | Honda CT90 / Trail 90 (K1-K8)

Replacement Carburetor & Main Jet Kit | Honda CT90 / Trail 90 (K1–K8)

If your CT90's original carburetor is beyond saving — corroded float bowls, stripped threads, missing parts — this is the replacement. We tested dozens of aftermarket carburetors marketed as CT90 replacements and found most are the wrong design, poor quality, or lack parts support. This specific version is the most accurate replacement for the original Keihin two-screw float bowl carburetor used on K1 through K8 models. It fits, looks, and operates like the factory unit.

Why You Need This

Many CT90 carburetors can be saved with a rebuild kit, but some are simply too far gone — seized slides, warped flanges, cracked bodies, or missing altogether. Barn-find Trail 90s often come with no carburetor at all. The aftermarket is flooded with replacements that don't match the original Keihin design, leading to fitment problems and poor running. We've done the testing so you don't have to.

This carburetor comes ready to install with a #65 main jet and #35 idle/pilot jet — the factory stock jetting for most K1–K7 models. A complete main jet tuning kit is included so you can dial it in for your specific environment.

Features

• Pull-out altitude compensation knob
• Integrated fuel screen and petcock — "O" mark is run position, "R" mark is reserve
• Quick float bowl drain screw
• Installed jetting: #65 main jet, #35 idle/pilot jet
• Five-position adjustable slide needle

Specifications

Included Main Jet Kit

• #62 Main Jet
• #65 Main Jet
• #68 Main Jet
• #70 Main Jet
• #72 Main Jet

Honda used different main jet sizes across CT90 production years. The K1–K7 models came with either a #62 or #65 main jet from the factory, and the K8 (1977) used a #62. The included jet kit covers the full factory range plus one step richer (#70, #72) for bikes with intake or exhaust modifications.

Does NOT fit: Honda CT90 K0 (uses a 4-screw float bowl carburetor — completely different design) or CT90 1978–1979 models (uses a round float bowl carburetor). These models require different carburetors.

Installation

Difficulty: Intermediate

1. Shorten the drain barb — Before installing, cut approximately 1/4 inch off the carburetor bowl drain barb. This is required for proper clearance with the engine case. Do not skip this step.
2. Install the new top cap and slide assembly — Mount the new top cap, slide, needle, and return spring onto the throttle cable as a complete assembly. Do not reuse the top cap, slide, needle, or return spring from your old carburetor.
3. Mount to intake manifold — Do not overtighten the carburetor to the intake manifold. The casting can strip or the flange may bow, causing an air leak.
4. Set the fuel petcock — The "O" mark on the fuel inlet barb is the run position. The "R" mark is the reserve position.
5. Adjust idle — With the engine at operating temperature, set idle speed to 1,300 RPM using the throttle stop screw. Adjust the air screw to find the smoothest idle — the factory base setting is approximately 1 turn out from fully seated on K8 models.

Jetting tip: Start with the installed #65 main jet for most riding conditions at or near sea level. If the bike runs rich (black plugs, poor throttle response), step down to the #62. If it runs lean at higher altitudes or with intake/exhaust modifications, step up to #68 or #70.

Frequently Asked Questions

Does this carburetor fit my 1967 Honda CT90 K0?

No. The CT90 K0 uses a completely different 4-screw float bowl carburetor design. This replacement is only compatible with K1 through K8 models (1969–1977).

Does this fit the 1978 or 1979 CT90?

No. The 1978–1979 CT90 models use a round float bowl carburetor (identification mark B27A), which is a different design from the K1–K8 two-screw float bowl style this carburetor replaces.

What main jet should I start with?

The carburetor comes installed with a #65 main jet, which is the stock size for most K1–K7 models. The K8 (1977) used a #62 from the factory. Start with the installed #65 and adjust from there based on how the bike runs — black spark plugs mean too rich (step down), white/lean plugs mean too lean (step up).

Can I reuse the slide and needle from my old carburetor?

No. Install the new top cap, slide, needle, and return spring as a complete assembly on the throttle cable. Using old internal components in the new carburetor body can cause poor fit and air leaks.

Do I need to cut anything before installing?

Yes — the float bowl drain barb must be shortened by approximately 1/4 inch for proper clearance with the engine case. This is a required step before installation.

You Might Also Need

• Carburetor Rebuild Kit — CT90 K1–K8 — for bikes where the original carb is salvageable
• Carburetor Gasket Kit — CT90 K1–K8 — replacement gaskets and seals
• Carburetor Float — CT90 — if your float is waterlogged or damaged
• Air Filter Element (Foam) — CT90 — a dirty filter affects jetting
• Throttle Cable — CT90 — replace if frayed or sticky
• Clear Poly Fuel Line (5.5mm) — replace old cracked fuel lines while the carb is off

Last updated: March 2026