Carburetor Float Level Gauge | Honda CT90 through CB750
A purpose-built float level gauge for setting carburetor float height on vintage Honda motorcycles. Stamped from steel with laser-etched millimeter markings, this gauge gives you a fast, repeatable measurement every time you rebuild or adjust your carburetors. It works on all Honda models from the CT90 Trail 90 through the CB750 — any Keihin carburetor with a measurable float.
Why You Need This
Every carburetor rebuild requires setting the float height. The float controls how much fuel sits in the bowl — set it too high and the engine floods, set it too low and it starves for fuel at higher RPMs. Honda specifies a different float height for nearly every model, and getting it wrong causes noticeable running problems.
This gauge is adjustable for a wide range of carburetor styles. It is marked in centimeters (1, 2, 3) with each millimeter noted in between. To read a spec like "21 mm," look for the mark just past the "2" line.
How to Use
- Remove the float bowl from the carburetor body.
- Hold the carburetor with its main bore vertical so the float arm tang just closes the float valve without compressing the spring-loaded pin inside the needle valve.
- Position the gauge on the gasket sealing surface and read the measurement at the highest point of the float.
- Compare your reading to the factory specification for your model (see chart below).
- To adjust: Remove the float pin and gently bend the small metal tab on the float hanger that contacts the float needle. Bending the tab inward lowers the mm reading (raises the fuel level); bending outward raises the mm reading (lowers the fuel level).
For carburetors with two floats, measure both sides — they should read the same. If one side is off, the float hanger may be bent or twisted.
Specifications
| Spec | Detail |
|---|
| Material | Stamped steel with laser-etched markings |
| Scale | Millimeters (0–30+ mm range) |
| Fits Models | CT90 / CB100 / CB125 / CB175 / CB200 / CB350 / CB360 / CB450 / CB500T / CB350F / CB400F / CB500K / CB550 / CB750 (all CL, SL, CJ variants) |
| Sold As | Individual gauge |
Honda Factory Float Height Specifications
These are the factory-specified float heights for each model. Always measure from the gasket sealing surface to the top of the float, with the float tab just touching the needle valve without compressing its internal spring.
| Model | Float Height | Notes |
|---|
| CT90 K0 (early, 1966–1968) | 21 mm | Early K0 carburetor |
| CT90 K0–K8 (1969–1977) | 20 mm | Standard round float bowl |
| CT90 (1978–1979) | 10.7 mm | Late model round float bowl |
| CB100 / CB125 | 24 mm | |
| CB175 / SL175 / CB200 / CL200 | 21 mm | |
| CB350 / CL350 (early square float) | 19 mm | "Bread loaf" style float |
| CB350 / CL350 (late round float) | 23 mm | Honda never updated the manual for the round float — 19 mm applies to the early square float only |
| SL350 K1–K2 | 26 mm | Round-slide carburetor |
| CB360 / CL360 / CJ360 | 18.5 mm | Factory spec; 16–16.5 mm preferred (see CB360 rebuild video) |
| CB450 / CL450 / CB500T | 20 mm | |
| CB350F / CB400F | 21 mm | Four-cylinder models |
| CB500K / CB550K / CB550F | 22 mm | |
| CB550 K3 / K4 | 14.5 mm | PD-style (round-slide) carbs |
| CB750 K0–K6, F1–F2 | 26 mm | |
| CB750K (1977) | 12.5 mm | PD-style carbs |
| CB750K / CB750F (1978) | 14.5 mm | PD-style carbs |
Our Honda CB350 Carburetor Rebuild Part 3 video demonstrates the complete float height measurement and adjustment process step by step — including how to bend the float tab and why both sides must read the same.
Frequently Asked Questions
Can I use a digital caliper instead of this gauge?
Yes — a caliper works for measuring float height. The gauge is faster for repeated measurements and shaped to sit flat on the carburetor gasket surface, which makes it easier to get a consistent reading across multiple carburetors.
My CB350 manual says 19mm but my floats are the round type. What do I use?
Honda published the float height spec for the early "bread loaf" square float but never updated the manual when the round float was introduced. For late-model CB350 / CL350 carburetors with round floats, 23mm is the correct target. This is a common source of confusion — our CB350 Carburetor Rebuild Guide covers the difference in detail.
How do I know if my float height is off?
Symptoms of incorrect float height include fuel overflowing from the float bowl drain or overflow tube (float set too high) and fuel starvation or hesitation at higher RPMs (float set too low). If you have rebuilt your carburetors and the bike still runs poorly, recheck your float height.
Does the gauge work on non-Honda carburetors?
The gauge reads in millimeters and is adjustable, so it will physically work on any motorcycle carburetor with a measurable float. The float height reference chart on this page is Honda-specific.
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Last updated: March 2026
