1984 Nissan 720 4x4 Weber Carb Problems

[RatsunSam]

  I decided to go out and buy a 32/36 Weber carb for my 84 Nissan 720 z24.  With the original carburetor I was getting pretty good gas mileage and average of 20 mpg. Once I installed the new Weber carb I was hoping to get a little more power and better fuel economy. But I was only going 180miles on one tank which is terrible.  Does anybody have any suggestions of why I could be getting such terrible gas mileage. Also thought I let you know that I have the fuel air mixture at 1 1/2 turns out. Also I noticed the idle fluctuates a little. Could someone please help me out.

[datzenmike]

Is the electric choke connected? and is it opening fully when warmed up?

 

Air fuel turns of the screw are pretty much useless except as a general starting point to get the engine started. Idle mixtures are adjusted by the owner and are probbaly different for every one. Too many variables like altitude, temperatures, engine condition, gas used summer/winter etc.  

 

A used weber is sometimes sensitive to too high a fuel pressure and will flood. 

[RatsunSam]

Yea the electric choke is connected but the anti - dieseling solenoid is not. And the plate moves straight up when warmed up.

 

 

 

 

 

[RatsunSam]

🤔

[RatsunSam]

Also datzenmike what color is the choke power wire and the solenoid wire 

[datzenmike]

Choke is Blue wire. Idle cut is Red.

 

Look down the carb while idling. Do you see any gas dripping?

[DIY 1985]

Where did you get your Weber?  Was it part of a Z24 Kit?

[RatsunSam]

I bought the carb off eBay for about $300 it’s a office Weber has all the badging. Yes it was a z24 kit and fits. The battery in my truck is starting to go can that cause the bad gas mileage ? I realize that I might sound stupid 

[DIY 1985]

A battery won't ruin gas mileage.  I had to tune my Weber to altitude.  I did it with an O2 sensor and readout.

[bottomwatcher]

Yep to properly tune you will need a wideband o2 sensor. Old school was while running shut off and read plugs. No need for that now and with fuel costs a wideband will pay for itself.

[RatsunSam]

Can my O2 sensor be bad and cause the bad gas mileage?

[datzenmike]

 The fact that you have a weber means that if this truck originally had the electronic controlled carburetor (ECC) which is controlled by an ECU under the driver's seat and an O₂ sensor, it's not doing anything now.

 

 

[Charlie69]

I pass emissions testing every 2 years here in Phoenix AZ with my Weber 32/36.  I have the oxegen sensor, the cat and the EGR all working.  The Weber 32/36 is the only carb I run on my Datsun/Nissan 4 cylinder engines.

 

When I buy a new to me truck the first thing I do is put a new Weber carb on it.  Then I can trouble shoot the rest of the engine.

[RatsunSam]

Another question my choke on the Nissan 720 z24 with the Weber is not working to very well. The connection is good some times it work other times it doesn’t. The automatic choke adjustment which way it’s better in colder climates? Also it hard to kick down sometimes and been doing it Manually. So could it be the choke relay?

[datzenmike]

Hold the throttle half open and turn the outer case of the choke heater. The choke flap should close. The problem is that it isn't very cold right now so you will probably need to adjust richer or more tightly closed in the winter.

 

Choke should warm up in under 5 min. Maybe it's just sticking? Spray everything down with WD-40 and work the linkages while holding the throttle about half way open to release the fast idle cam.You need a 12v supply to make the heater warm up and turn off. A test light touched to the wire at the choke heater will confirm you have power. The engine HAS to be running for this.

[Charlie69]

My O2 sensor went bad a couple of years ago, I changed it I was able to pass emissions.  Same with the cat and the EGR.

[datzenmike]

The O₂ sensor can't work with a Weber carb. It's a mixture feedback signal to the ECU under the driver's seat that sets the opening and closing of the solenoid  activated primary jet in the ECC carb. The Weber won't have this. It's good that it passed though.

[DIY 1985]

If your Air/Fuel Mix screw is 1.5 turns out, how many turns is your Idle Speed Screw in?  Are your plugs kinda black?  Are you running vacuum advance to the distributor?  If so, where is it plumbed into on the Weber?

[datzenmike]

On 8/2/2019 at 1:06 PM, datzenmike said:

 

 

Air fuel turns of the screw are pretty much useless except as a general starting point to get the engine started. Idle mixtures are adjusted by the owner and are probbaly different for every one. Too many variables like altitude, temperatures, engine condition, gas used summer/winter etc.  

 

 

 

Variations in carburetor mixture screws, the 'tune' of your engine, temperature, timing, humidity, idle speed makes setting your mixture solely on the number of turns impractical. The same applies to the idle speed.

[RatsunSam]

Also the battery light is on , went to  o’Reillys to check the alternator they said it was good. I put a new alternator belt  tightened it. I also put a new battery cause before the battery only lasted little more than a year.weird. But after doing all of this the battery light is still on.But I’m only putting out 12v and the needle on the gauge is shaking. Also when I put on the brake I hear a clicking coming from behind the glove box. It’s  Deming  other things to light up the brake lights. Could the   Alternator Be starting to go out?  I realize as it gets older it’s probably not gonna put out as much. This is what I think is linked to the  Electric choke not working properly, as it says it needs 12v to power it. In another forum I saw you say Datsun mike to test the battery from the alternator while it’s running correct? Any way sorry for so many questions ...

 

[RatsunSam]

Also DIY 1985 I am not running my vacuum advancing  distributor could that be causing it to run rich?

[datzenmike]

Proper charge is about 14v when running. Red charge light means no or very low charge. Alternator tests probably don't add any load to the alternator so it might 'test' good but still fail to do the job. Be sure your connections are snug and the plastic two wire plug is in good shape.

 

Running rich is probably the choke not shutting off fully because the alternator isn't charging.

 

If you have vacuum advance I would connect it and use it.

[RatsunSam]

Alright I tested my alternator and it was not charging my battery. I put a new alternator, new belt, new battery, cleaned the connections. I made sure the belt was tight. After that my battery light went away in my 720. I test my battery and still with all of that it’s not charging my battery still.

what now?

it is still showing 12v

[datzenmike]

1/ An experiment.... Loosen a battery terminal. Start the truck. Briefly disconnect the battery terminal. If the truck dies then the alternator is not charging. If it keeps running (this is a good thing) replace the cable and tighten then go to 2/ below....

 

2/ Connected to the positive battery post are the fusible links. They are wires about 3" long with plastic plugs on each end so they can be unplugged and replaced if needed.. The '84 should have three, 2 Green and a single Black. All are connected to the positive battery post and send power to various parts of the truck. When the alternator is charging, the Black link allows power back into the battery to charge it up and keep it charged. Use a volt meter on all the other ends of the fusible links, they should all read 12v because they are connected to the positive post. Perhaps the Black one is blown, perhaps the plugs are corroded and not making good contact.                                              

[RatsunSam]

 All right we tested number one we unhooked a battery terminal which in this case we unhooked the positive side. As soon as we unplugged it the truck died. So the refurbished alternator is not good?