1980 Datsun 720 Carburetor option

[Sergio146]

Hello,

My name is Sergio and I currently own a late 1980's Datsun 720 that I am on the lookout for the original carburetor. Right now it has a Weber carburetor with a manual choke which I definitely want to remove since it is terrible (Even After a rebuild) and cannot set up the idle correctly. All in all, I don't want a Weber Carburetor and I'm not looking for any performance upgrades. I want this truck to be reliable for everyday use, runs properly and I wanted to ask if this carburetor would fit my particular setup. Here are some things about the truck that I forgot to mention: It is an Automatic (188k), It has an L20B engine with a Nikki mechanical fuel Pump, and is a King Cab model. Also, I am aware of wiring the anti-dieseling solenoid and the choke (which both have to be fed ~12V when turned to the ON position which I have found two connectors that feed up to 11.68V when doing so). Right now this is my engine layout:

 

And this is the carburetor that I want to make sure would be compatible to fit in the truck: https://www.ebay.com/itm/80-Nissan-Datsun-720-Pickup-Truck-L20-Carburetor/264695917803

 

Anything is much appreciated. 

[Sergio146]

This is an old picture that had the electrical fuel pump, but I converted it into a mechanical fuel pump.

[]2eDeYe]

I am not sure you want to replace a marginally working carburetor with on in unknown condition.

A new or remanufactured carb would be a better idea. 

 

https://www.ebay.com/itm/HITACHI-2BBL-CARBURETOR-FITS-1974-1977-DATSUN-620-L20B-1952CC-ENGINE/402728771535?fits=Make%3ADatsun&epid=179444092&hash=item5dc4815fcf:g:we0AAOSwsPZgQS1q

[]2eDeYe]

And welcome, would love to see some more pics of the truck 🙂

[Sergio146]

ok, I see. Also looking into the carburetor that you suggest, where does the part on the bottom of the distributor (its a vacuum hose I think) go to in the remanufactured carburetor? Does it go on the side of the BCDD?  

[Sergio146]

Also, I'm curious if being an automatic would cause any issues in adjusting the carburetor since the remanufactured specifies in being a manual transmission? Just want to know if it matters or not. As you may know I'm new to this and being my first vehicle purchase with a carburetor, I am willing to take the challenge to fully understand how these cars/trucks work.

 

[Sergio146]

wouldn't this one be another candidate when considering a remanufactured carburetor?

https://www.ebay.com/itm/HITACHI-2-BBL-CARBURETOR-DCH340-FITS-1980-DATSUN-720-PICKUP-L20B-ENGINE/274714909009?hash=item3ff648d951:g:Yx0AAOSwl29gSPhu

[datzenmike]

You don't have a mechanical fuel pump. It's an electric mounted on the passenger side outer frame just forward of the rear wheel.

 

 

The stock carburetor you are looking to buy has two ported vacuum sources on the valve cover side. The one closest to the front on the truck is the distributor vacuum advance.

 

The other one is for the EGR but it appears that a previous owner has removed the EGR manifold and probably put on a home made block off plate. This is alright only if done properly because this also deletes the PCV valve. The new block off plate needs to be drilled and tapped to accept a PCV valve. Can you take a picture of the driver's side of the carburetor??? Looks like the previous owner has just joined the block vent and the valve cover vents together. A pox on previous owners and their ignorance.

 

You will need a stock air filter housing to get the ATC (automatic temperature control) working if you live anywhere where it drops to freezing, to prevent carburetor icing.

 

 

The automatic choke and the idle cit solenoid wires should be there although once again the previous owner probably cut them off short. On the 620 trucks with the same engine the two wires come from the coil area.

[Sergio146]

For the picture on the driver side of the carburetor:

 

As for the Air filter housing, would this one work? https://www.ebay.com/itm/Datsun-620-Pickup-Truck-Air-Cleaner-Assembly-Breather/324498621321?_trkparms=aid%3D111001%26algo%3DREC.SEED%26ao%3D1%26asc%3D20160908105057%26meid%3D289e4d1b14754d1ab81f5331c1cfc7e9%26pid%3D100675%26rk%3D1%26rkt%3D15%26mehot%3Dnone%26sd%3D324498621321%26itm%3D324498621321%26pmt%3D0%26noa%3D1%26pg%3D2380057%26brand%3DNissan&_trksid=p2380057.c100675.m4236&_trkparms=pageci%3A3d2d09b5-877f-11eb-8f92-1eed3905e9c1|parentrq%3A42b131bd1780a12b7cf175c5ffd299ba|iid%3A1

 

And for the PCV valve, which one would be useful in putting in the truck?

[Sergio146]

I'm sorry if I was not clear but the photo in the beginning is old and was before I installed the mechanical fuel pump. Previously, yes it had the electric fuel pump installed.

[datzenmike]

Understood.

 

Yes the PCV valve is missing and the hoses a mess. There's no where to put the PCV thanks to the previous owner. You could look for the missing EGR manifold it will have one on it.

 

 

Not a good picture but you can run it without the EGR working. The rusty fitting middle right is where the hose from the block vent connects. The hose from the valve cover goes to the stock air filter housing.

[Sergio146]

Ooh, I see Intresting. Actually come to think of it, does this manifold fit my truck? It says that it came off of a 79 datsun 620 but with an L20B (which I have) but when I removed the Plate next to the carburetor, the entrances are the same. It also looks like the EGR valve and PCV valve are included as you have mentioned previously.

https://www.ebay.com/itm/1979-DATSUN-PICKUP-L20B-ENGINE-EGR-VALVE-PARTS-1978-1977-1976-1975-1974-OEM/164175308436?hash=item26399c6694:g:EywAAOSwCFBepY~m

 

Also, I have a questions about the white plate in the back whether it serves a purpose and if the spring thing on the middle left side has to do anything with tuning the original carburetor once it is in place?

 

[datzenmike]

The exhaust is bolted to the underside of the intake. This uses exhaust heat to warm the intake below the carburetor to help evaporate gas when the engine is cold. The spring with the weight on it is to block this off when the engine is hot. They seldom work right and seize either shut so it's no use or full open so it bakes the intake. The metal around it is a heat shield. 

 

 

I see that your engine is from a '75-'77 something. That isn't an '80 engine.

[Sergio146]

Ok. Now that I know this, what would be your suggestion when considering a carburetor of this engine?

[datzenmike]

15 hours ago, Sergio146 said:

wouldn't this one be another candidate when considering a remanufactured carburetor?

https://www.ebay.com/itm/HITACHI-2-BBL-CARBURETOR-DCH340-FITS-1980-DATSUN-720-PICKUP-L20B-ENGINE/274714909009?hash=item3ff648d951:g:Yx0AAOSwl29gSPhu

 

13 hours ago, Sergio146 said:

 

 

 

As for the Air filter housing, would this one work? https://www.ebay.com/itm/Datsun-620-Pickup-Truck-Air-Cleaner-Assembly-Breather/324498621321?_trkparms=aid%3D111001%26algo%3DREC.SEED%26ao%3D1%26asc%3D20160908105057%26meid%3D289e4d1b14754d1ab81f5331c1cfc7e9%26pid%3D100675%26rk%3D1%26rkt%3D15%26mehot%3Dnone%26sd%3D324498621321%26itm%3D324498621321%26pmt%3D0%26noa%3D1%26pg%3D2380057%26brand%3DNissan&_trksid=p2380057.c100675.m4236&_trkparms=pageci%3A3d2d09b5-877f-11eb-8f92-1eed3905e9c1|parentrq%3A42b131bd1780a12b7cf175c5ffd299ba|iid%3A1

 

And for the PCV valve, which one would be useful in putting in the truck?

 

The carburetor above will work but the price is practically a new one. Still if it is what it says saves in the long run. The air filter housing below that will work.

 

You can run without the PCV for now and maybe the easiest course of action is to buy a new valve and drill and tap that block off plate for it.

[Charlie69]

I would personally get different intake and exhaust manifolds (unmarried).  That price for a"rebuilt carb" is rediculious.  Is there a core charge on top of the $399?

 

Do you need the smog control for passing emissions?

 

Here is my 1976 L20B with a cannon intake manifold with the crankcase vent pipe plumbed to thePCV valve with the stock rubber tube.

 

This is the factory I believe 1976 exhaust manifold. mike can probably confirm year or post correct exhaust manifold information.

 

This Cannon intake manifold is available through Pierce Manidfolds and uses the Weber 32/36 DGV seires carb. The cab on your engine is a Weber DGV-5A manual choke carb.  This is an older maodel Weber.  Pierce manifold also sells new weber carbs and also Weber rebuild kits and other parts.   The weber DG series carbs are simple carbs to rebuild and maintain.

 

I run the Weber DGEV 32/36 carbs on all my Datsun/Nissan trucks.

Edited March 18, 2021 by Charlie69

[datzenmike]

 

This style, 4 into 2 were used on the L16/18 with the exception of the very first use of the L20B on the '74 610.  The L16/18 style break down into two subsets. One pairs cylinders 1 and 4 together just behind 2 and 3 just in front. Both pairs remain separate down to the down pipe connection. The other is like the one above and although there are two outlet pipes the cylinders are not kept separate.

 

Separate pairs.......................................................................................................................... not separate

 

All other years of L20B (including the 610) were 4 into 1 with the '75-'77 co-joined to the intakes. The '78-'80s had round instead of square exhaust ports and the manifold was separated from the intake.

 

'75-'77 co joined 4 into one L20B

 

'78-'80 L20B 4 into 1

 

 

 

 

 

 

 

[Sergio146]

ok, So far I have obtained an EGR manifold for the part that would fit on the side of the Intake. For the rest of the parts, how does all the hoses go on when installed in the truck? I  don't quite understand how all the hoses should go. 

 

[datzenmike]

At the end of the day all you really need the EGR manifold for, is the PCV valve.  You can connect the block vent pipe to it and away you go.

 

 

[Sergio146]

Ok, Thanks Mike. I appreciate you helping in understanding this mess that I'm in. Hopefully this will change how my truck Idles since right now it Idles like crazy and it is too fast for it to be revving up to almost 2,000 RPM's. 

[datzenmike]

That will be something else. The PCV continuously sucks combustion gasses out of the crankcase and draws in fresh air. This removes water and gas vapors that condense when the engine cools and dilutes the oil. This extends the oil change interval and prolongs engine life. In the 50s you would be very lucky to get 100k out of any engine.

 

Fast idle possible causes.....

 

 

Fast idle set toooo high

 

Fast idle cam stuck on, possibly choke stuck on causing this. Look down the carburetor when engine warmed up, is the choke plate closed / part closed or is it fully vertical and open?

 

Throttle cable toooo tight. Can't return to proper idle.

 

Carburetor throttle shaft worn in body and throttle plate rubbing and sticking in the bore. Usually a quick stab of the gas will dislodge it.

 

 

[Sergio146]

I will look into this. For the EGR manifold, when I installed it with all the vacuum lines plugged,(except for pcv valve and another one that is facing 30 degrees up) the engine ran upon startup,but then stalled. The engine vent tube was connected to the 30 degree nipple and the pcv had nothing connected. Did I connect something wrong? Or do I need to install a Hitachi carburetor for it to work?

[datzenmike]

 

The very bottom hose with the kinks on it connects to the PCV. The hose on the valve cover can be left connected directly to the Weber for now. When you get a stock air filter it connects to it.

 

This is the PCV valve....

 

 

The block vent pipe (silver) goes to it.

 

[bilzbobaggins]

https://nationalcarburetors.com/1980_c_1275.html

 

I used these folks 8 years ago.  My carb worked great after my failed attempt at fixing my carb.

 

edit:  I see its a r&r service anymore.  Dont help you as you dont have a carb to be worked upon.  damnit

Edited March 24, 2021 by bilzbobaggins