Carb problem

[datzenmike]

Take the fuel line off and loosen the bolt holding the banjo fitting and unscrew and take the needle valve holder out. There should be a fine mesh screen in there too. Maybe something obvious will present itself.

[Datsun pickup]

Would the condition of the mesh screen effect anything? Cause this is the condition of my mesh screen.

[datzenmike]

If torn open or missing then some debris may have gotten in and is jamming the inlet needle from closing.

[Datsun pickup]

The needle valve holder is brand new. Can anyone send a picture of how the float and needle should be set?

[datzenmike]

New maybe but that screen is no good. Either someone had it apart or the carburetor is a cheap knock off. Just unscrew the inlet needle valve holder from the carburetor. It should be self evident how it goes together. The needle valve is held up in place with a wire clip. There's no adjustment for it.

 

Any adjustment is done to the float below it...

 

 

18 hours ago, datzenmike said:

On the vehicle.... place rags under front of carburetor to catch the gas in the float chamber.

 

Loosen/remove the three screws on the front of the carburetor. Pull the front cover off.

 

Watch for and collect and save the tiny brass spacer on the end of the hinge rod that the float swings on. It holds the float away from the glass. The rags should catch it if it falls off. If it stay on perhaps take it off and safely save it.

 

Lift the float up using a pencil till the needle valve above it just barely bottoms out. The top surface of the float should be horizontal and parallel to the ceiling of the float chamber at this point. If you can measure it, the top of the float to the top inside of the float chamber should be about 0.28". To adjust, bend the tang that contacts the needle valve. Don't forget the small brass spacer when assembling. 

 

If it is good or if after adjusting it still floods then maybe the needle valve has something stuck in it and can't close fully.

 

 

Usually the float is set holding the carburetor upside down so take this into account. Try to get the top of the float parallel with the top of the float chamber. The proof that everything is set correctly is when the fuel level is at the mark on the glass on the front. Adjust as needed.

 

[Datsun pickup]

Which float should I have? The one on the top or the one on the bottom.

Edited April 11, 2022 by Datsun pickup

[datzenmike]

11 hours ago, datzenmike said:

Usually the float is set holding the carburetor upside down so take this into account. Try to get the top of the float parallel with the top of the float chamber. The proof that everything is set correctly is when the fuel level is at the mark on the glass on the front. Adjust as needed.

 

 

I could only find this diagram but like I said it's usually set with the carburetor upside down with the float hanging down with the needle valve closed. Yours will be right side up so you will have to lift the float carefully with something like a pencil to close the needle valve. Make the adjustment if needed so that the float is parallel with the top of the float chamber.

[Datsun pickup]

Does anyone know where I would be able to get a mesh screen?

[datzenmike]

16098-H7201 try the Nissan dealer. Doubtful but you never know. Try auto parts store.

 

https://www.nissanparts.online/oem-parts/nissan-filter-16098h7201

 

https://www.amayama.com/en/part/nissan/16098h7201

 

https://www.monotaro.sg/p/64599718.html

 

 

[Datsun pickup]

Everything with the float and needle is working, except the float is not floating. I think there is too much pressure above the needle seat. Would anyone have an explanation on this?

[datzenmike]

There is a needle valve that lets fuel into the float chamber. As it fills, the float is lifted and it pushes the needle valve closed shutting off the fuel. If the float is not rising... is the float chamber filling with gas???

 

1/ Excessive fuel pressure will make closing the needle valve harder to close, but this is unlikely.

 

2/ There may be dirt caught in the needle valve and the float cannot close it.

 

3/ The float may be set too high and is no effectively closing the needle valve.

 

4/ Some floats are hollow brass. If they leak the sink and can't float up and close the needle valve. I think the 720s are solid black plastic.

[Datsun pickup]

The float chamber is filling up with gas. The needle works just fine. Is there a tool to adjust the float? I tried adjusting it, but nothing has worked.

[datzenmike]

Is it at the dot on the glass? or very close? That's fine. More than 1/8" above or below I would try to get closer.

 

You bend the tab that rests against the needle valve.

[Datsun pickup]

There is a problem with the wiring in between the starter relay and the carburetor. When I touch or move the carburetor the starter relay clicks.

[datzenmike]

On the standard transmission there is no starter relay. The ignition switch start signal is wired directly to the starter solenoid.

 

On automatic trucks the start signal from the ignition switch is controlled by the transmission interlock switch and an inhibitor relay to prevent the starter working in any other gear position than Park and Neutral. There is no connection to the carburetor.

 

The clicking must be something else.

 

You should not be able to move the carburetor. It should be bolted down to the intake.

[Datsun pickup]

The choke heater makes the ignition relay click. I am also not getting spark to the engine. What would cause the engine to not get spark and the choke to not work properly?

[Datsun pickup]

I have two problems with my carb right now.
 

The choke heater is heating up, but the spring is not coiling up.

 

the float is adjusted, but fuel is not getting past the needle.

[datzenmike]

The spring will unwind when heated and the choke releases to the off or fully open position.

 

Can you hear the fuel pump working?

 

Inside the banjo fitting where the fuel line connects to the carburetor there is a very fine mesh screen. Remove the banjo fitting and check it is not clogged. If ok now you can unscrew the fitting that holds the needle valve and check that it is free to open. If both are good then the float must be set too low.

 

 

[Datsun pickup]

The spring in the choke heater is not unwinding, or moving at all.

 

My mesh screen is all torn up.

[datzenmike]

Take that fitting out and make sure it isn't plugged up with trash.

 

Is the fuel pump working? can you hear it?

[Datsun pickup]

Yes the fuel pump is working. Could you show a picture of how the float should be seating?

[datzenmike]

Basically when lifted up GENTLY don't force it, to it's highest position it should be horizontal. The correct way means taking carburetor off and turning upside down, then the float top (now the bottom) should hang down to 0.28" from the top inside of the float chamber.

 

Once adjusted confirm that the running fuel level is at the horizontal line on the glass front (older models) or the dot on the round glass on the front of the float chamber. Adjust as needed to get this.

[Datsun pickup]

I have my float adjusted properly, but the fuel pump does not stop, so the bowl fills up with fuel. Would the fuel pump have anything to do with my problem?

Edited July 4, 2022 by Datsun pickup

[Datsun pickup]

How do you adjust the idle? It is currently idling at about 2,250 rpm. Is that normal?

[datzenmike]

no

 

 

 

Have you tried turning the idle speed screw down?

 

Is the choke on? There is a fast idle function that it engaged while the choke is on. Warm the engine at least 15 min. and then take the air filter top off and look. If the choke plate is not vertical then this is a possibility.

 

This...

 

 

Not this...

 

 

It is possible the choke is off but the fast idle circuit is stuck on.

 

It's possible that the secondary throttle plate is not fully closed.