Rochester 2 Jet Float System

How the 2 Jet Float Works

2 Jet Float Circuit

The carburetor float system controls the fuel level in the carburetor bowl. Fuel level is very important, because it must be maintained to give proper carburetor metering throughout all ranges of engine operation. If the fuel level is too high in the float bowl, problems such as rich mixtures, fuel spillage from the main discharge nozzles on turns, and engine loading can result. If the fuel level is lower than the specified setting it can cause lean mixtures, hesitation on acceleration, engine surge plus engine cut-out during heavy fuel demands.

The float system operates as follows:
Fuel from the engine fuel pump is forced through the fuel inlet screen or filter, and on through the float needle seat, past the float needle, into the float bowl. Fuel flow continues until the fuel raises the float pontoon to a position where it forces the float needle against the float needle seat and shuts off fuel flow.

As fuel is used from the carburetor bowl during engine operation, the float again drops downward moving the float needle off its seat, allowing more fuel to flow into the float bowl, thereby, keeping the fuel level consistent.

A float drop tang located at the rear of the float arm prevents the float from moving too far downward. The maximum float drop must be maintained so that the float assembly will drop sufficiently to allow maximum fuel flow under heavy engine fuel demands. Some models use a float needle pull clip which is attached to the float arm and connected to the float needle valve. The purpose of the pull clip is to pull the float needle off its seat, should it stick closed due to dirt or gum formations.

Rochester 2 Jet Float Adjustment (includes Mercarb)

Float level specifications are different depending on carburetor number and application. There is no one fit all measurement.

Float Level Adjustment
  • Bowl gasket in place.
  • Plastic float – measure distance from gasket tolip of free end of float.
  • Brass float – measure distance from gasket to sharp edge of float seam at free end.
  • We set the float to be level, which works great for us.

2 Jet Float Drop

Float Drop Adjustment

With float hanging freely, measure from gasket surface to lip of plastic float, or bottom of metal float.

Check the float drop to make sure the needle doesn’t fall out, or gets stuck to the side.

Here is a remark from one of our Youtube watchers:

A few years ago I had a condition where the float drop was too low. Had a failing fuel pump which allowed the float to bottom out when the engine was under load. Then when normal driving resumed, the needle valve jammed because it was pulled too far out of the valve body. Result was a flooded engine with raw fuel pouring out of vent into carb inlet. Got religion, always check the float drop.

Rochester 2 Jet Carburetor Parts
Holley 1920 Carburetor Manual
Updated on 10/10/2021

Was this article helpful?

Related Articles

Need Support?
Can't find the answer you're looking for?
Contact Support