Carb problem

[Datsun pickup]

I have a 1985 Nissan 720 with z24 motor, the carburetor has a rhythmic backfire when trying to start. How would that be fixed?

[Thomas Perkins]

32/36 Weber,with idle cut off solenoid...and jet.And 0-ring for solenoid,don't come with it...

Edited April 3, 2022 by Thomas Perkins

[datzenmike]

Have any of the plug wires been off?

 

Distributor cap may be worn out, cracked or otherwise damaged and spark is jumping to the wrong wire. Visually inspect the cap inside and out for cracks or carbon tracking.

[Datsun pickup]

I have a hitachi carb. Some of the spark plug wires have been off, and the distributor cap is brand new. Is there something else that could be wrong?

[datzenmike]

Did the back firing start after the wires were off? Seems like they should all be checked. There's 8 a lot of chances to get two of them wrong.

 

 

More info.

 

Is this something that just started happening?

 

Is this a new vehicle for you and you have no history on it?

[Datsun pickup]

It is something that just happened, although is was backfiring before, but not rhythmic. It is a new vehicle for me. I do have history on it, but it was just regular maintenance and inspections.

[datzenmike]

Backfires when trying to start.

 

Does it backfire when driving?

 

 

 

Well check that the plug wires go to the correct plugs first. Easy and doesn't cost anything.

 

Next check the valve lash. Should be 0.012" for intake and exhaust. A tight intake can do this.

[Datsun pickup]

I fixed all the valve lashes that were a little off and it doesn’t backfire anymore!

[Datsun pickup]

It cranks but doesn’t start. I don’t think the engine is getting fuel. What would my problem be?

[datzenmike]

It was getting enough fuel to backfire.

 

 

Was it running? Have you ever had it running??? If it was running this narrows down the possibilities. If it's never run then it can literally, be anything.

[Datsun pickup]

It has run before but, didn’t run right. I was trying to put starting fluid in the carb to start it but it wouldn’t start. Fuel is not coming out of the jet.

[datzenmike]

Is there gas in the tank?

 

Look at the front of the carburetor, at the sight glass. Fuel level should be visible half way up.

 

Turn the ignition on while having someone listen in front of the rear passenger side tire where the electric fuel pump is. Do you hear it running??? The 15 amp fuse for it is the 5th one over to the right from the left hand side of the fuse box.

[Datsun pickup]

Yes, there is gas in the tank and there is gas visible through the sight. The fuel pump is running but it is very loud. Could that mean a bad fuel pump?

[datzenmike]

They are not silent so any sound just means it's working.

 

If gas in the carburetor then fuel is being supplied.

 

 

Take the air filter off and work the throttle while  holding the choke plate open and looking with engine off. You should see a strong squirt of fuel from the accelerator pump.

 

Is your choke on????? or closed???

 

Choke open

 

Choke closed

[Datsun pickup]

I did not see gas come out of the accelerator pump. I think there could be something wrong with the accelerator cable, because the throttle plate didn’t open or close when I pressed the accelerator pedal.

[Datsun pickup]

There is gas coming out of the accelerator pump, and I think the accelerator cable is good. The secondary throttle diaphragm assembly is not working as it should.

[datzenmike]

You should be able to see the primary throttle plate open fully into the vertical position.

 

The secondary is pulled open by vacuum when the engine is sufficiently revved up and under load.

 

 

Did you check the choke? On a cold engine it should close till started. Take a look.

[Datsun pickup]

The choke valve does not close when cranking, and there is gas puddling in the intake manifold. Should there be something sucking gas into combustion chamber?

[datzenmike]

Two more things wrong....

 

1/ choke should be closed when engine is cold and for starting.

 

2/ gas should not puddle in the intake:

 

Are you pumping the gas pedal when starting? Once or twice is enough for starting. More, or continuing to pump will flood the engine making starting very difficult. Avoid pumping the gas. Hold throttle 1/2 open and turn engine over with starter to clear the excess gas. You might even take the exhaust side plugs out (because easier to get at) and spin the engine over to dry it out inside. If the exhaust plugs are wet with gas take the intake side out as well and dry them. Try again and avoid pumping the gas it will only make things worse.

 

[Datsun pickup]

I mostly haven’t been pumping the gas.

[datzenmike]

Well the puddle came from somewhere and if what I said, it's fixable. If the carburetor is over flowing that's worse.

[Datsun pickup]

The fuel pump pumps gas to the carb and the float bowl overflows and overflows the carb.

[Datsun pickup]

I think that the float needs to be adjusted. How do I adjust the float? What is float drop and float level? Can the float be adjusted with the carburetor attached to the engine?

[datzenmike]

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.

[Datsun pickup]

The needle will not seat correctly. I don’t know what is wrong.