Carburetor Replacement and EGR Removal

[chatpey]

Hi,

 

I’m looking to replace the carburetor on my Datsun and I’ve been considering a Weber kit from California Datsun. I recall hearing that this company doesn’t have the best reputation around here—is that still the case? Do you have any recent experiences or alternative recommendations?

 

Also, I’m planning to remove all the EGR components since I’ll be installing the Weber. Is this a good idea, and is it a tricky process to do myself?

 

Thanks for your advice!

[datzenmike]

California Datsun.... no. 

 

Pierce Manifolds still distributes genuine Weber carburetors. As far as I know these Weber carburetors are actually Made In Spain so check that out.

 

 

There is absolutely nothing to be gained from removing the EGR valve. It only works above idle when the engine is warmed up. It is not working at idle and full throttle so has no effect on performance... none. If you don't want it, just pull the vacuum line off of it to disable it. The problem with it's removal is the hole in the intake must be sealed with a home made cover plate and gasket and if not done right this can cause a vacuum leak that is hard to find. The best outcome is to just leave the EGR alone.                

[chatpey]

Thanks for your help.

I will order https://www.piercemanifolds.com/product_p/k660.htm

[datzenmike]

Genuine Webers are manufactured in Spain. I would look there first.

[banzai510(hainz)]

You live in Spain???????

I think you could get a Carb there as they are made in Spain.

[chatpey]

made in Spain but cheaper in USA... globalization 😞

[Stinky]

Also, Amazon

 

https://www.redlineweber.com/carb-kits/auto/nissan-truck.html

[chatpey]

Hi all,

 

I'm working on my 1977 620 (L20B, California truck) — installing a Weber 32/36 DGEV and doing a full de-smog at the same time. I've annotated a photo of my engine bay and have a few questions before I start pulling things.

 

 

**Points 1, 2, 3, 4 — air injection tubes on the exhaust manifold**
From what I've read on this forum (topic #47208), the correct plug is a 3/8" brass flare plug — is that confirmed for all four holes? And do I need to remove the metal rail connecting them first, or can the tubes be unscrewed individually?

 

**Point 5 — small fitting on the intake/exhaust area**
There's a plastic fitting here that is broken. Can I just cut it flush ? Or do I need to plug it too ?

 

**Point 6 — breather on the valve cover**
With the original air box gone (Weber has its own filter), should I add a small breather filter here to keep the PCV circuit working properly?

 

**Points 7 and 8 — leaving as-is?**
Point 8 appears to go back to the charcoal canister — I understand I should leave that circuit intact. Is point 7 also part of that circuit, or something else?

 

**Point 9 — EGR valve location on intake**
My Weber kit came with a block-off plate for the EGR port — I'll use that. Anything specific to watch out for when installing it?

 

**Point 10 — vacuum hose that used to connect to the original air box**
With the stock air box gone, where should this hose go?

 

**Point 11 — air pump (smog pump)**

Once the air injection rail is removed, the smog pump has nothing to do. I'd like to remove it for a cleaner engine bay. Does it share a belt with the alternator or water pump on the '77 L20B? Anything to watch out for before pulling it?

 

Thanks in advance — this forum has already been incredibly helpful through the search function.

 

chatpey

[datzenmike]

 

Do you need to pass any smog test???? Any removal of parts or tampering will be an automatic fail.

 

1,2,3,4.... Probably easier to cut the tubes then use a socket to remove the fitting then plug the holes.

 

5.............. Is the TVV. I removed and plugged.

 

 

6...... do not plug. There is a plastic elbow fitting from Weber that you can buy and connect this up. Those trendy little filters are stupid. Any blow by escapes and will find it's way into the cab. Do it right!

 

7....... is the Anti Backfire Valve. Air from the air filter is directed into the manifold at fitting8. Up to you but without it there will be unnecessary and annoying back firing into the exhaust on deceleration. I would keep functional, it has no effect of running.

 

8..... is connected to intake vacuum and draws stored gas fumes from the charcoal canister. You only have one vacuum advance port on the Weber so splice the  hose in front of the upper radiator hose into the vacuum advance hose to keep the canister functional.

 

9.....  EGR delete plate needs a gasket. This is connected to intake vacuum and must not leak!

 

10..... This is the 'stove pipe' that allows heated air to the ATC auto temperature control. This is the vacuum servo on the original air filter housing controlled by a thermal sensor inside and prevents carburetor icing in near and below freezing temperatures. The intake air is maintained at about 100F so the engine drives like it's summer all year round. Just leave it and if you have your original air filter and have drive ability problems in the damp and cold you can modify the bottom so it fits the Weber and keep it functional. There should be a vacuum line from the original housing to the intake, probably at 8.

 

11..... No need for the air pump now, so remove. It's on it's own belt. Easy enough to see this by looking.  

[banzai510(hainz)]

he in spain. I would just leave it on there, but weber on and adapt.

 

plugging holes might not be worth it

 

I dont think they had L motors in europe. Maybe greece    L 14s

Edited May 9 by banzai510(hainz)

[chatpey]

Thanks a lot for the detailed answer, very helpful!

 

A few follow-up questions:

**1-4** — Can the tubes be unscrewed without cutting first, or is cutting really necessary given how corroded they usually are? I'll try without cutting first if there's enough access.

 

**6** — Good news, the plastic elbow is included in my Weber kit. I just need a short piece of hose to connect it to the valve cover breather. What diameter should I look for?

 

**7** — With the original air box gone, the Anti Backfire Valve has no air source anymore. Should I leave its intake open to the air, cap it, or try to connect it to the Weber filter somehow?

 

**8** — If I understand correctly: since the Weber only has one vacuum port (used for distributor advance), I need to splice a T-fitting into that vacuum line so both the distributor and the charcoal canister purge are fed from the same source. Is that right?

 

**9** — Got the gasket covered, thanks.

 

Thanks again!

[datzenmike]

Spain??? 

 

How'd I miss that, baby? 

 

 

 

 

 

 

 

1-4 fittings I found were very soft for a spanner. They squashed so I changed to cutting tube off and using a socket.

 

6... measure the valve cover fitting width and get hose with same inner hole diameter

 

7... I think the air should be filtered as it goes into the engine. Maybe one of those cute little air filters?  

 

These are 43mm opening, might fit. $13 on Amazon for two. 

 

 

8.... correct. Usually they have separate. 

[chatpey]

Hi again,

 

Following up on the previous answers — I've found the Messer diagram for the '75-'77 California L-series vacuum system, which helped me understand the full picture.

 

 

**BCDD (point 16) — keep or remove?**

The BCDD prevents stalling/stumbling on hard deceleration by cracking the throttle open when manifold vacuum spikes. On the original carb it connects to a dedicated port (point 2 on the diagram). Does the Weber 32/36 DGEV have a suitable port to keep the BCDD functional? Or do most people just remove it without noticing any deceleration issues on the L20B?

 

If the BCDD can't be kept, the five-way junction (12) goes with the rest of the smog equipment. Which leads to the only remaining question:

 

**Intake manifold vacuum fitting (point 7 on the Messer diagram)**

 

With everything removed, should this port be plugged, or can it be left open? It was previously feeding the five-way junction — with that gone it has nothing connected to it.

 

 

**Vacuum circuit — distributor + canister**

From my photos I can see there is already a T-fitting in the vacuum line between the Weber and the distributor, with a branch going down to the charcoal canister. Just confirming this is correct and nothing needs to be changed there.

 

(vacuum routing — green trace shows the existing T circuit)

 

Thanks again for your patience!

[datzenmike]

First of all the California emissions system is the most complicated and has the most emission controls of all. Many are not on other trucks including hoses. It will likely just confuse you.

 

BCDD should be left alone. 

 

#7 if left open is a vacuum leak. It must be sealed off.

 

I couldn't tell in your previous picture but yes the vacuum advance hose can also be used to work the charcoal canister. Definitely, the canister should be kept functional. It's function is to store evaporated gas from the tank and allow it out to be sucked into the intake when the engine is running. It also serves to vent the gas tank and allow air in as the fuel level drops. It has zero effect on running and performance.

 

 

[Stinky]

#6 I have one of these on my 720.  They no longer make it in the correct size.  I think, as in, maybe, that I have a K&N filter on my other truck.

 

They are on Amazon.  I got these at Oreilly and Autozone....which I assume doesn't help you out one little bit.

 

https://www.autozone.com/p/spectre-engine-crankcase-breather-element-3991/415841?searchText=spectre+filter&productPartGroupId=azpg1538&productBrandId=BGCX&productUniqueId=6584195233

[datzenmike]

#6 appears to be a vacuum delay for the EGR. This prevents short term applications of EGR from short term vacuum spikes from throttle applications. My 710 has one on the vacuum advance for the distributor. (removed when EI installed) Later 720s have small BBs in the vacuum lines that do the same thing.   

[chatpey]

Hello,

I've ordered 3/8" flare plugs and a similar air filter (apparently made for motorcycles) for the back firing valve :

[chatpey]

Hi again,

 

Some progress today, and a few new questions.

 

**Anti-backfire valve — sorted**
Managed to fit a 13mm breather filter directly on the valve with a hose clamp. Clean and functional.

 

 

**EGR tube on the intake — gasket damaged**
Removed the EGR tube from the intake to take out a block-off plate that had been installed by a previous owner. Got it out but the gasket suffered in the process. Need to replace it.

Two questions:
1. Is there a part number for this gasket, or a standard size I can match?
2. If I need to make one — what material should I use and what thickness?

 

 

 

**Air injection rail — tubes too corroded to unscrew**
The tubes are heavily corroded and I can't unscrew them. I'd prefer not to cut them as I want to keep the parts in good condition as much as possible. Looking for an alternative approach. I'm thinking of finding a plug to replace the check valve directly — would that work? What size/thread would I need for the check valve port? If no one has the info, I'll take both parts to a hardware store to match the thread.

 

 

**Intake manifold vacuum fitting (point 7)**
The fitting is a different size than the air injection tubes — the 3/8" SAE flare plugs I ordered are too big. I'm considering using a short piece of hose to loop the two EGR outlet ports together on the intake instead of plugging them individually. Would that be a valid solution? If not, what is the correct thread size for this fitting? I'll also bring the part to a hardware store to match if needed.

 

 

Thanks!

[chatpey]

Hi all,

 

Following up on my previous questions. Here's where things stand and a few new ones.

 

**Resolved since last post**

- Intake manifold vacuum fitting (point 7): M1/4" plug with PTFE tape — to be confirmed
- Air gallery transfer tube: G1/2" plug (20mm OD) with PTFE tape — to be confirmed
- EGR gasket (14720-U6700): not available individually in Europe. Fabricated a replacement from a 1.6mm reinforced exhaust manifold gasket sheet with metal backing — rough cut for now, will redo properly

 

**New questions — throttle linkage**

I now have the Weber 32/36 DGEV on the bench. I removed the throttle cam and bracket from the old Hitachi (see photos).

 

   

 

 

 

My understanding from reading other threads is that these original pieces should replace the universal linkage plate included in the Weber kit :

1. Is it a direct fit ?
2. Where exactly does the return spring attach — between the bracket and the throttle lever? Any tips on getting the geometry right?

3. Does the Weber bracket need to be bent or notched to get the cable properly aligned with the shaft? I've seen ACTippets (YouTube) mention he had to notch his bracket to get the cable closer to the firewall.

 

Thanks again for all the help so far!