Float Circuit Illustration
The pull clip is used to help pull the needle out of the seat thus preventing sticking. Hang the clip anywhere on the float so that the needle pulls straight up and doesn’t get pulled to one side. CAUTION: Do not place a pull clip through small holes in the top of the float arm. Severe flooding will result.
On non marine the fuel inlet filter will be either 1″, or 2″ long. It’s easy to determine which one by looking at the inlet fitting. The open end of the filter should be toward the fuel line. The spring is inserted into the inlet 1st. The filter should have a check valve built in to prevent fuel from flowing back to the fuel pump.
Replace the fuel filter at minimum once each year.
Be careful not to put any pressure on the needle when adjusting the float. The viton tip is easily damaged.
Test your needle & seat to make sure it is sealing.
The seat may or may not have windows in the side to allow gas to flow sideways. Both work just fine and it depends on the manufactures preference.
There are two types of float needle valves used in the Quadrajet carb. One type is diaphragm assisted and the other is the conventional needle & brass seat.
The diaphragm assisted float needle (shown in the right inset in the illustration) is used primarily with a smaller float and on engines equipped with high-pressure fuel pumps. The needle seat is a brass insert and is pressed into the bowl fuel inlet channel below
the diaphragm needle tip. The seat is not removable, as the needle valve tip is of a material which makes seat wear negligible.
Care should be used during servicing so that the seat is not nicked, scored, or moved. The float valve is factory staked and tested and should not be re-staked in the field.
Fuel flow through the diaphragm assisted float needle valve varies from the conventional float needle. With the conventional type as shown on the left in the illustration, fuel flows from the inlet filter and inlet channel up through the needle seat orifice past the
float needle valve and spills over into the float bowl. With the diaphragm type float needle valve, fuel from the inlet filter enters the channel above the float valve tip. When the fuel level is low in the bowl, the needle valve is off its seat and fuel flows down
past the float valve tip into a fuel channel which leads upward through the bowl casting to a point above the normal liquid level and spills over into the float bowl.
The diaphragm type needle valve differs in operation from the conventional float needle in that a larger needle seat orifice can be used to provide greater fuel flow to the float chamber and yet allow the use of a small float. This is accomplished through a
balance of forces acting on the float needle valve and diaphragm against fuel pump pressure. Fuel pressure entering the float needle valve chamber tends to force the needle valve closed. However, the same pressure is also acting on the float needle
diaphragm. The diaphragm has a slightly larger area than the float needle valve head, therefore the greater pressure acting on the diaphragm tends to push the needle valve off its seat. The force of the float arm acting on the needle stem, as the float bowl fills,
overcomes this pressure difference and closes the needle valve. Therefore, the float’s function is to overcome the pressure difference and it does not have to force a needle valve closed against direct fuel pump pressure as does the conventional needle type.
The conventional float needle seat on some Quadrajet carburetors has holes or “side windows” in its side whose purpose is to supplement fuel delivery past the float needle valve when it opens, whereas the “side windows” have been removed on some
float needle seat applications so that all fuel will be discharged over the top of the needle seat assembly. Removal of the “side windows” improves operation of the float needle on some applications.
Some conventional float needle seats are nickel plated and use a double angle seat. The double angle seat, along with use of a less resilient Viton tip float needle, aids in preventing the float needle from possibly sticking in the seat due to fuel gum formation.