Jump to content

Emissions delete - not how but why

Recommended Posts

I see a lot of the threads about ripping out the emissions stuff on our 720s but, looked for, and couldn't find post(s) by Datzenmike that suggested that doing so wasn't necessarily the best idea and may not help in the long run in some cases.


This is a request to Datzenmike to see if he would repost the thread(s) detailing what the purpose of each of the emissions add-ons is and how they affect driveability, etc. but anyone can certainly chime in.


Getting ready to take off my old Hitachi carb on my '86 Cal emissions z24 and replace with the Weber 32/26.  I am reluctant to remove the carbon canister for starters because I think the fumes have to go somewhere, right? Blocking off the vent line from the tank doesn't seem like the wisest idea. There is a fitting on the Weber for the vapor vent from the canister. I'm not sure what else on that system needs to stay to be sure that the vapor goes into the engine.


I've already blocked off my EGR. I couldn't bring myself to buy new EGR tubes after replacing my exhaust manifold because I snapped off an exhaust pipe bolt.


What about the rest of the stuff?  I assume that some has to go because I'm removing the Hitachi but I'm not totally comfortable with ripping everything out without knowing why.

  • Like 1
Link to post
  • Replies 10
  • Created
  • Last Reply

Top Posters In This Topic

Top Posters In This Topic

Posted Images


1/ What you loose switching to the Weber first of all it the stock air filter and the ATC. With some work you can cut the bottom out and make a new one that allow it to fit the top of the Weber. The Automatic Temperature Control regulates the air supply by mixing cold air from in front of the rad with air heated by the hot exhaust using vacuum to pull against a spring door in the air snorkel. This maintains the air at about 100F. At below zero the engine thinks it's August and runs accordingly. The warmed air will evaporate the fuel easier and improve the driving during the warm up period and lessen unburned gas in the exhaust. Without it, at near freezing, the metal carburetor is super cooled by gas evaporation to well below freezing and dampness (fog, freezing rain) can collect as ice on the venturi plugging it and the engine slows and stalls. What about better performance needing cold air you ask??? well when floored the intake vacuum drops to near zero and the spring loaded ATC closes off the warm air and only air from in front of the rad is used. 


The stock air filter also has a temperature activated air bleed to the intake to compensate for an over rich idle mixture due to extreme under hood temperatures in the summer.


So there are 2 reasons not to switch to a Weber... or what to do to keep the stock air filter working. 



2/  Exhaust gas has no oxygen and is basically inert and just takes up space. When added to the intake in small and varying quantities it takes the place of some gas and air to reduce peak cylinder temperatures that are the cause of oxides of nitrogen. People won't admit it but they think that somehow the EGR is ripping them off and reducing their performance and removing it will be an improvement. All you will do is make more nitrogen oxides than you have to. There is no EGR at idle. The engine can't burn this weak mixture. There is no EGR during warm up and no EGR at full throttle because it is activated by vacuum and vacuum is too low a full throttle to open the EGR valve. It's best to leave alone or just pull the vacuum hose off to deactivate it. Removal requires that you seal the hole left on the intake: often done poorly and a vacuum leak is the result.


Charcoal Canister

3/ Simply stores gas fumes so they don't escape into the environment. When engine is running these fumes are drawn into the intake and burned. Has absolutely no effect on running. Completely benign.



4/ A system using a small amount of intake vacuum to draw moist gasses and combustion bow by out of the crankcase and into the engine for burning. Make up air is drawn into the valve cover from the air filter. If blow by under load exceeds what The PCV can handle it reverses out the valve cover hos and into the carburetor. It extends the oil change interval and an engine will last at least twice as long with it. No effect on performance and is completely benign in operation


Fuel Shut Off

5/ When slowing from high speed with the throttle closed the idle mixture is not needed and just goes out the exhaust pipe. Using clutch, throttle position and gear position switches the idle cut solenoid can be deactivated to cut fuel from the idle circuit. Actually saves gas.



6/ The Thermal Vacuum Valve when cold has two open air bleeds that destroys the ported vacuum signal to the EGR and the Vacuum advance during warm up. When warmed the valves close and vacuum will begin to operate the EGR and advance. Some California hoses have built in delays or small restrictions to slow their use and prevent sudden or short term applications of vacuum.


Catalytic Converter (if equipped)

Simply put, burns air and unburnt gas at mixtures that wouldn't normally ignite and burn. Works in conjunction with the AIS (Air Injection System) using exhaust vacuum pulses to draw in filtered air (oxygen) from the air filter through one way reed valves and introduces it into the exhaust manifold. Has no effect on running.



There's lots more but these are some of the main ones. Removal is not going to make your engine perform better and likely it will run worse.


  • Like 2
Link to post

Nice write up Mike. Mike I can count on my one hand how many times driving any of my Datsun/Nissan trucks that I was running along at WOT.  Now my old hot rods when I was younger yes I ran them at WOT a lot either street racing or playing with cops.


With the law enforcement presence being cut back on a regular bases I see street racing becoming even more prevalent.

Link to post

Thanks Mike, That is what I was looking for. I like the idea of using the stock air filter and have been in contact with mklotz to get advice on how he did it. The main issue for my switching to the Weber is that my choke doesn't work now and cold morning startups take a long time. I just need to figure out how and where to draw the vacuum needed to run the air filter components. I also hear that the Weber filter is noisy compared to the stock air filter and that is also important to me. My truck is loud enough now. I plan on keeping the charcoal canister and PCV.  Sounds like the TVV and Fuel shut off are history. I know Weber sells an idle cut-off solenoid but with the rest of the ECCS essentially disabled I'm not clear on what tells the Weber cut-off solenoid to operate

  • Like 1
Link to post

Test for 12v on the choke wire while the engine is running. Engine has to be running. If nothing there, a new carburetor won't help much.


Put a universal manual choke in it. Way easier and cheaper than a $300 Weber kit..

  • Like 2
Link to post
37 minutes ago, Ooph! said:

"The main issue for my switching to the Weber is that my choke doesn't work now and cold morning startups take a long time."




Auto Choke.jpg

Thanks, I saw these. The choke is the main issue but I also seem to have to adjust my idle more frequently than I would like as it won't stay adjusted over time. I decided that I didn't want to deal with drilling out the rivets for a carb that was probably on it's last legs. 

  • Like 1
Link to post

I disagree w.the egr delete.


I've know several people that track their mpg and have noted a dif.  Also, it will be more likely to ping if deleted.


One of the negatives of the Weber is the air filter.  There is a thread here, somewhere, about a guy that made a base for the Nissan housing, to go on the Weber.  This gives you cold air intake, which is a significant benefit and also a better filter.  Cold air for the carb made a dif of 4 mpg on my Toyota powered VW bus.  Every car made today has it....cuz it works.

  • Like 1
Link to post
48 minutes ago, matrophy said:

Thanks, I saw these. The choke is the main issue but I also seem to have to adjust my idle more frequently than I would like as it won't stay adjusted over time. I decided that I didn't want to deal with drilling out the rivets for a carb that was probably on it's last legs. 


Weak arguments for spending $300 on a Weber. Is your ATC working? Seasonal outside air temperature variations would explain the idle changes. The EGR needs to be wire brushed clean every 30k. If not crud can build and prevent it closing perfectly at idle. There are lots of things that would explain the idle even variations in gasoline quality. The speed screw does not change it's adjustment nor the mixture screw.


EGR: At the same speed the EGR equipped engine will have the throttle slightly more open that the one without. This is to make up the slight difference in power removed by the displacing of fuel and air by recirculated exhaust. On the EGR equipped engine the throttle is open wider and the engine has less work to do pulling air past the resistance of the throttle plate.

Link to post

Thanks DM, Wouldn't be the first time that I acted before having all of the information, I guess.

  • Like 1
Link to post

Absolutely get the Weber if you want. Depends on what you expect to get from it. 

  • Like 1
Link to post

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

  • Create New...

Important Information

By using this site, you agree to our Terms of Use.