Adjusting Float Height—

To adjust float height:

1. Remove float bowl orings or gaskets stuck to carburetor body. If they separated with bowls, leave alone.

2. Tilt the carbs at about 45 degree angle, or just enough to allow floats to touch the float valves (AKA: fuel or needle valves).

3. Do not allow the floats to compress the float valve pin & spring when measuring.

4. With the metal adjustment tang on the float just touching, but not compressing the float valve spring, place the setting gauge or dial caliper over the highest part of the float.

5. In most applications, if the floats are different heights on the same carburetor (right to left); use the highest float (the one farthest away from gasket surface).

6. To correct the float height setting, bend the small metal tang, then recheck the measurement. Bend the tang a little bit at a time until you get the desired height. Floats must be within a .5mm (1/2mm) or .020" range of each other.

Why adjust the float height?

A carburetor is just a fancy siphon. The piston creates a vacuum that siphons gas out of the float bowl through the various jets. If the level is low, the bike will run lean because the gas must siphon too high on a given vacuum. If the level is high, it siphons too much and runs rich.

If the level is erratic (sticky float hinge) it can act lean, then rich, and back again driving you nuts.

If the level is way too high, the floats may not stop gas flow and the engine and air box may take on fuel. Gas may flow until the tank runs dry. Some carbs have overflow tubes so it just runs out on the ground.

Changing the float height changes the level of the fuel in the float bowl. Fuel height adjusts: full throttle, 2k-3k rpm or partial throttle cruise. To give a scale of change, if the bike runs well when cold, but gets a bit sloppy when fully warmed up, lower the fuel level 1mm (i.e. go from 15mm to 16mm float height - remember the float measurement is "backwards").

Setting the fuel level on a carb with adjustable float heights is the way to jetting perfection. A too high or too low of a fuel level will cause the engine to run too rich or too lean at low rpm cruise and at full throttle / 3k (on sport bike) or 2k (on cruiser).

When do I adjust the float height?

When installing a Carb Recalibration Kit
When rebuilding carbs (if necessary)
To adjust low rpm areas of throttle operation that isn't pilot jet, fuel screw, or needle height related.
When a bike starts running rich at low RPM