Need help with my Dads 1981 720

[Jared55b69]

Hello all I have a 1981 Datsun by Nissan  720 4 x 4 pick up that belong to my father before he passed away. It sat for 14 years and my brother finally brought it to me in Oklahoma all the way from Oregon. Don’t really know a lot about it, but I do know a lot about cars. And trucks I got it running new plugs, wires, oil, fuel, and it ran, but it idled really high. I was just mainly wondering about putting a new carburetor on it and what type to get and all the crazy vacuum lines. Also, I was wanting to know a way to lift it up two or 3 inches for more clearance and a Bigger tire. I would like to know what kind of seats will fit in the truck because the ones in there are garbage so if anybody could point me to a service manual or any info or direction would be amazing. I would love to pay honor to my dad and get this thing on the road again. He loved this little truck. I started on the body work but I want this little engine to scream lol. It has the z22 engine and is pretty stock. It fired right up once I put new fuel in. It just idles high and dies when you accelerate. I’m not sure of the timing or vacuum configuration so I thought I would save some time by asking you amazing folks for your help!! thank you all for your help.

[NC85ST]

On 1/10/2025 at 10:49 PM, Jared55b69 said:

I want this little engine to scream lol.

It will scream, but don’t expect it to go fast. As far as a different carburetor, a Weber is a good replacement. You can get rid of most of the vacuum lines. Bigger tires will make it slower than it already is. Keep up the good work.

[Jared55b69]

Is there anymore engine upgrades that can be done. Also is there somewhere that tells me which vacuum lines to get rid of. Lol 

[datzenmike]

Not really any upgrades as the Z series of engines have built in impediments to performance increases. What you can do is get it running in top shape. 

 

Fast idle is likely the choke is stuck. Once warmed up take the top off the air filter and look. Choke plate should be vertical an fully open like this...

 

 

Not partly or fully closed like this...

 

 

Use only NGK spark plugs, never use fram oil filters, run Shell Rotella T4 oil in 10w30 as this has the required ZDDP levels that are no longer available for our older gas engines. Set valve clearances to 0.014" on a hot engine, timing around 5 degrees.

 

 

 Post a few engine pictures. May be easier to point out what could and what you shouldn't remove. Hose removal won't change anything if expecting this to improve thngs. In a lot of cases it can cause problems.

[NC85ST]

You could swap in a z24, but that’s not much of an upgrade. If you’re swapping carb’s, you can get rid of all but one vacuum line to the carburetor. The one for the vacuum advance on the distributor. If not, replace all the vacuum lines to make sure they’re not going to cause you any problems. You can look at this thread if you decide to go Weber, same year truck as yours.

[ElliotV]

You really only need to keep the vacuum advance and the brake booster on a Weber swap but it could be beneficial to leave a couple more hooked up. On the passenger fender there should be two vacuum switches, one is for the exhaust spark plug shutoff and the other is a fuel cutoff. I am unsure exactly how the fuel shutoff works if it's tied to the carb or the fuel pump with the computer or if they had them on a 81 I know my 83 has one and my 85 but my 86 doesn't have it and it has a Holley 5200(Weber clone) and runs fine for essentially a jalopy. The vapor canister is another one worth leaving hooked up as well. 

 

As for a lift on these trucks 4x4parts.com makes upper control arms to correct the ball joint angle to do a 2-3in lift. You technically don't need them because the torsion bars are used to set suspension height but they will save your upper ball joints and correct camber angles. Your truck looks like someone might have already cranked the torsion bars. Biggest tire I have seen someone fit is 31s but you might be able to get away with 32s if you run a pizza cutter such as 235/85r16.

 

Redline Weber makes a 32/36 conversion kit with the brackets and carb adapters needed and can be ordered online or you can order one from bughaus in Tulsa. You said you are in Oklahoma and I even called them the other day to see if they can get Weber parts for me and the conversion kits and they said they can usually get them in next day(although not right now with the fires in Cali some stuff may be delayed). 

[Thomas Perkins]

Here are the vacuum switches.They are still.on mine.Both hoses go into one hose and that hose goes into one of the ports in the intake maniflod.Other port coming out of intake is blocked.Does need to be used with Weber.I have my 85 Nissan 720 service right here.it has switch A(Z24) switch B.It says they are used in a high altitude model only with a altitude switch which is by the Fuel pump relay.So I could disconnect mine.Also says for the M.P.G.Model.Here is another showing vacuum.switch A.Here is something else on the the High Altitude.I never paid any attention to this since it says for high altitude.It also matters how you have your wiring on both coils.It shows the wiring from the ecu going to the Intake - coil .See.Check out they show the wiring to both coils.

[Thomas Perkins]

Here is a picture showing how the wiring is to the ignition coils.They are not color coded.If you notice the exhaust  coil  + has a fuse in it.

Edited January 12 by Thomas Perkins

[ElliotV]

Thomas also has videos of his hose routing for his Weber 32/36 on his YouTube channel. 

[datzenmike]

11 minutes ago, Thomas Perkins said:

Here is a picture showing how the wiring is to the ignition coils.They are not color coded.If you notice the exhaust  coil  + has a fuse in it.

 

The fuse is in the fuse box and is on the far left side.

[Jared55b69]

You guys are awesome! I thought about putting a 350 small block in it. But I also kinda want to keep it original. Where can you get that book? I will post engine pics Mike! 

[Jared55b69]

 

[Thomas Perkins]

Here is the wiring for the ignition coils.The exhaust coil has a red wire on the -.Black wire with white stripe goes to +.Intake coil.Brown wire goes to +.White wire with blue stripe goes to -.Get your coils from Auto Zone.Lifetime Warranty.Had them.over 5 years.Stay away from Orielly's.Their's corroded on the inside.

 

Edited January 13 by Thomas Perkins

[Jared55b69]

Ok, dumb question. I’m new here and olí don’t see how to add anymore pics lol  

[datzenmike]

Oil pan would have to clear the front differential and the Nissan transfer case wouldn't handle 3X the power. SBC would make more sense in a 2wd but even then it won't fit. Radiator would have to be remotely mounted in the box or firewall cut out and engine moved back. There goes the heater and comfort. There are an infinite number of way to fuck this up and it's a one way trip to the scrappers, and only one or two to get it right.

[ElliotV]

4 minutes ago, datzenmike said:

Oil pan would have to clear the front differential and the Nissan transfer case wouldn't handle 3X the power. SBC would make more sense in a 2wd but even then it won't fit. Radiator would have to be remotely mounted in the box or firewall cut out and engine moved back. There goes the heater and comfort. There are an infinite number of way to fuck this up and it's a one way trip to the scrappers, and only one or two to get it right.

The big thing would be the oil pan and pickup clearing. But it's a tight fit side to side for a SBC from what I've seen people do on the 2wd trucks. These transfer cases are actually surprisingly stout. There was a discussion on I believe the pirate4x4 forum about a guy with a SBC straight axle swapped 720 that used the divorced case and the only time he ever broke one was when he rolled the truck for the 12th time or something and he was known for beating on his stuff. Id say that's pretty stout. I'm going to run them on my 86 and use one backwards for two outputs when I make it 6x6 whenever I get around to it. They will probably get swapped out for np205s' but that won't be until it's straight axle swapped with 80 series axles and a diesel but even then it will take effort to shred it likely. 

[Thomas Perkins]

I can not say if using the vacuum lines like I have it set up is better than deleting them.I only know from how I have it set up runs Awesome.Its a 4x4 and as we know it is not made to be a fast ride.It does run better without the cat.More power to me.My tires are 235-75-15.I tried 31's and they rubbed real bad and I am not going to lift it.

Edited January 13 by Thomas Perkins

[ElliotV]

Just now, Thomas Perkins said:

I can not say if using the vacuum lines like I have it set up is better than deleting them.I only know from how I have it set up runs Awesome.Its a 4x4 and as we know it is not made to be a fast ride.

I'm unsure how the two vacuum switches on the wall work with the Weber and no electronic carb but I also don't know if when people remove them the exhaust plugs stay working. Never seen any discussions on it but I believe it is for the plugs to shut off from what I can tell when they receive ported vacuum so maybe they just stay on.

[Thomas Perkins]

Are you front tires straight up and down.Not leaning in at the bottom.

[ElliotV]

31s you need the correct offset. My 86 has 31s and they don't rub but the offset is much farther out than the stock wheels. I have 235/75r15 all terrains on my 85 that it came with when I bought it just over a year ago and they have been good especially for a 80 dollar a piece tire. 

[datzenmike]

19 minutes ago, ElliotV said:

I'm unsure how the two vacuum switches on the wall work with the Weber and no electronic carb but I also don't know if when people remove them the exhaust plugs stay working. Never seen any discussions on it but I believe it is for the plugs to shut off from what I can tell when they receive ported vacuum so maybe they just stay on.

 

Under heavy throttle loads the engine makes an objectionable noise according to Nissan. This is likely the two flame fronts colliding in the combustion chamber. I don't think it harms anything but sounds like a diesel clacking away. To reduce noise, the exhaust side plugs are turned off by the distributor with a signal from a vacuum switch on the right inner fender. The vacuum signal is not ported but comes directly from the intake. Low intake vacuum = heavy load/throttle = turn the exhaust side plugs off. As this is a manifold vacuum source, switching to a Weber will not affect the exhaust side plugs turning on and off.

 

Now the beauty of dual plugs is that there are two points of ignition so the combustion is faster, taking less time and thus the ignition timing is later at around 3-5 degrees before TDC. When the exhaust side plugs are shut off the combustion takes a lot longer to complete so the timing has to be advanced to around 10-12 degrees to start the burn sooner and the distributor takes care of that as well.

[ElliotV]

1 hour ago, datzenmike said:

 

Under heavy throttle loads the engine makes an objectionable noise according to Nissan. This is likely the two flame fronts colliding in the combustion chamber. I don't think it harms anything but sounds like a diesel clacking away. To reduce noise, the exhaust side plugs are turned off by the distributor with a signal from a vacuum switch on the right inner fender. The vacuum signal is not ported but comes directly from the intake. Low intake vacuum = heavy load/throttle = turn the exhaust side plugs off. As this is a manifold vacuum source, switching to a Weber will not affect the exhaust side plugs turning on and off.

 

Now the beauty of dual plugs is that there are two points of ignition so the combustion is faster, taking less time and thus the ignition timing is later at around 3-5 degrees before TDC. When the exhaust side plugs are shut off the combustion takes a lot longer to complete so the timing has to be advanced to around 10-12 degrees to start the burn sooner and the distributor takes care of that as well.

Yes that's my bad should've wrote ported vacuum

 

Edit manifold vacuum my brain said manifold vacuum but my fingers said ported

Edited January 13 by ElliotV
Slow

[datzenmike]

You did...

 

1 hour ago, ElliotV said:

I'm unsure how the two vacuum switches on the wall work with the Weber and no electronic carb but I also don't know if when people remove them the exhaust plugs stay working. Never seen any discussions on it but I believe it is for the plugs to shut off from what I can tell when they receive ported vacuum so maybe they just stay on.

 

but you meant intake vacuum. The ported vacuum from the carburetor is for EGR and another for vacuum advance. Neither have any at idle and at full throttle. 

[ElliotV]

Alright I'm done for the night I think I can't even correct myself 

[Sephakrid]

On 1/12/2025 at 4:10 PM, Jared55b69 said:

You guys are awesome! I thought about putting a 350 small block in it. But I also kinda want to keep it original. Where can you get that book? I will post engine pics Mike! 

 

This directory has quite a lot of files, including a complete '86 FSM. It's a private Facebook group, but shouldn't be hard to join

 

https://www.facebook.com/groups/720Owners/files/files

 

I haven't been able to find a pdf of an '81 FSM yet!