Webers and Emissions Controls

[copacetickid]

disclaimer: I don't know shit, but I really want to learn.

 

I just bought a used weber 32/36 and in the process of figuring out how to install it I learned a few things about my '79 620's L20b. There is almost nothing on the right of the engine (when looking at it from under the hood) besides the master cylinder, coil, and horns. The air injection system is totally gone, including the air pump. And this may seem silly, but I can't find the crankcase to intake PCV hose (is there a hose??), let alone the valve it plugs into!! see first line. Everyone says the Haynes manual is the way to go, but I have one and find it sketchy on the details.

 

My question is about the weber carb: because of the shiny chrome air filters that almost always accompany them, does everyone disconnect basically every emission control component in their truck?? This also may be silly sounding, but that is not acceptable to me. It's trucks like mine with no ECs that cause a great deal of the air pollution out there. I don't care if it's exempt or not, I don't want to be spewing nasty shit into the air if I don't have to.

 

I'm planning on replacing as much of the EC components as I can, and I've seen air filter adapters from a weber to a stock air filter, but I don't know how much of the built-in EC components require the stock carb. Did I just spend $75 for nothing? Also, can any of you clue me in to how important each component of the EC system is? Why the hell would anyone unplug the PCV system??

 

If anyone has a stock L20b with working emissions controls, can you take a few pics of it for me to compare against? It would be MUCH appreciated.

[lancekilgore]

The pcv comes off the same plate as the EGR, the hose goes underneath the exhaust manifold and goes into the crank case .

 

I disconnected them and dispite what you think about the emissins and all that all the emmsision stuff does on thes old datsuns is break it up you still have the same amount going out into the air.

 

If you really want I could sell you a intake manifold with the airstuff aswell as the filter and pump and all. I won't use it.

 

You have to leave the pcv hooked up or you will cause engine problems you don't need.

 

I can't give you pics because mine is all apart waiting for the block and head to come back from the machine shop so I can rebiuld it.

 

Lance

[datsunaholic]

A picture won't help much, because so much is buried under everything else

 

 

Yeah, this is a '78 car, but the engine is essentially the same. I'd assume you're missing the air injection manifold, the air pump, the EGR valve, the BPT valve, the AB valve, and all associated plumbing.

 

Even if you were to find an air cleaner adapter for the weber, the air cleaner wouldn't clear the hood well. I've tried it. I have the rub marks to prove it.

 

I pulled the air pump belt off my '78 in 1993 when it still had to go through smog and it passed smog with better numbers than with the belt on, though that was probably due to the pump failing and loading the engine (because I also gained about 5MPG highway with it off). It is true that most of the smog components don't hurt anything be leaving them there (if working)- only the smog pump is parasitic.

[kiznook]

the standard redline rectangle filters have a hole and a bung for the breather. Of course on my car theres a duct tape patch there :D

[datsunaholic]

Yeah, I think he's looking for more than just the breather. The stock air cleaner in '78-79 had about a half-dozen vacuum lines as well as attachments for the AB valve plumbing and heat riser.

[datzenmike]

disclaimer: I don't know shit, but I really want to learn.

 

I just bought a used weber 32/36 and in the process of figuring out how to install it I learned a few things about my '79 620's L20b. There is almost nothing on the right of the engine (when looking at it from under the hood) besides the master cylinder, coil, and horns. The air injection system is totally gone, including the air pump. And this may seem silly, but I can't find the crankcase to intake PCV hose (is there a hose??), let alone the valve it plugs into!! see first line. Everyone says the Haynes manual is the way to go, but I have one and find it sketchy on the details.

 

My question is about the weber carb: because of the shiny chrome air filters that almost always accompany them, does everyone disconnect basically every emission control component in their truck?? This also may be silly sounding, but that is not acceptable to me. It's trucks like mine with no ECs that cause a great deal of the air pollution out there. I don't care if it's exempt or not, I don't want to be spewing nasty shit into the air if I don't have to.

 

I'm planning on replacing as much of the EC components as I can, and I've seen air filter adapters from a weber to a stock air filter, but I don't know how much of the built-in EC components require the stock carb. Did I just spend $75 for nothing? Also, can any of you clue me in to how important each component of the EC system is? Why the hell would anyone unplug the PCV system??

 

If anyone has a stock L20b with working emissions controls, can you take a few pics of it for me to compare against? It would be MUCH appreciated.

 

Here are three images of my '78 L20B emissions. Like yours the air pump was gone when I got it so all the pipes are mostly gone also.

 

OK here we go... In the first picture are two flattened round things, the one to the left (the BPT valve) is slightly lower than the other (the EGR valve). There is a rubber hose going into the top of the BPT valve (it's not shown well) but a separate one coming out and going to the EGR valve.

 

Now there is another valve in the thermostat housing (not shown) that allows carb vacuum to go to the BPT valve, BUT, only if the engine is warm. This is important!! If the engine is below a certain temp, there is NO vacuum to the EGR system and it is OFF. For the rest we will assume the engine is warm.

 

Continuing, at the bottom of the BPT valve is a small metal tube that is connected to the small manifold that the EGR is bolted to. This small manifold supplies exhaust gas from a pipe on the far right with a large fitting on it. If you look at picture two you will see a tapered fitting with a smaller tube. The obvious hose above it, is the PCV valve hose (more on it later). In picture three you can see the U shaped, finger size pipe below the PCV hose as it turns and is bolted to the exhaust manifold.

 

In operation, exhaust gases and pressure are supplied to the base of the EGR and BPT valves. The BPT (back pressure transducer) valve opens in relation to exhaust pressure and allows vacuum to be passed to the EGR valve which opens and allows exhaust up from the manifold and directs it toward the base of the carb where it mixes with the fuel and air. Recirculated exhaust gas is supplied in direct relation to exhaust back pressure. So... more throttle... more back pressure... more recirculated exhaust... simple.

 

If you want to NOT want EGR, simply remove the vacuum hose from the BPT valve in picture one, and put a plug in the end. No vacuum... no EGR. How bloody hard is that, for all those who have ripped everything off and have to make a block off plate. Then have no where to put the PCV hose and valve, so drill and tap a hole... so unnecessary.

 

OK, I'm back, with picture two. Positive Crankcase Ventilation. The large silver-grey hose is clamped to the PCV valve which is screwed into the manifold and shares the entrance into the intake with the recirculated exhaust gases. The PCV valve allows a measured amount of intake vacuum to draw fumes and water vapor from the crankcase through the rubber hose. But the valve prevents flow the other way. Obviously a backfire could ignite fumes in the crankcase and cause an explosion. I saw an early '60s Chevy with the valve cover blown off and the oil pan bent from this. Picture three shows the PCV hose curving downward to a metal pipe that connects to the inside of the block just under the exhaust manifold.

 

 

 

 

 

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[copacetickid]

Thanks for the pics dholic and mike! And may I just say mike, you're my fuckin hero.

 

So, every component you guys talk about is gone. And I don't feel so silly anymore for not being able to find the crankcase to intake manifold pcv hose... it's totally gone from my truck. That block off plate you were talking about mike? Well someone put one on my manny and instead of making a hole and tapping it, they decided to just pull off the pcv hose altogether... And the "plate" isn't really a plate as much as it is some kind of hi-temp putty in between a bolt and two sheered off studs. *sigh* There are two 1 1/2" holes in the side of the block that are plugged and one of them is underneath the exhaust manifold where it looks like the hose should go in your third pic. I don't even want to know how it was plugged... but I guess I'll find out when I replace it somehow.

 

I downloaded the '78 620 service manual from http://www.the620.com and found some good explanations of the emission controls. What I still would like to know is how effective each of the three (PCV, AIS, and EGR) sub-systems are. And by effective I mean how much of a difference do they actually make? Is lance right that it's not important to break up the pollution?

 

And back to my original question(s) about webers: on the rectangle air filters, is the "breather" where the valve cover to filter pcv hose goes? If not, what happens to it? And wtf is with the air control valve on the stock filter snorkel? Does the engine ever really want hot air? Mike: you told me in another thread that L20bs like a hot engine and cold air. With the rectangular air filters, do you just have to accept that the air temp going into the filter is ambient engine temp?

 

Lastly, and most likely related to all of this: after a bit of driving, the air in the cabin starts to smell fumy like the exhaust is somehow leaking in. All the air ventilation in the cabin I think comes through the cowl, and there are no holes that aren't plugged in the wall behind the engine... where is this coming from??

 

I'll take some pics tomorrow so you can get a better idea of what my engine looks like.

[copacetickid]

upon further inspection of this photo (thank you hainz), the holes I saw apparently have nothing to do with pcv. One thing is for sure though, there's no hose coming from where it should.

[datzenmike]

I think the PCV valve is essential to clean running. With out it gas, oil and water vapors condense inside the engine when it cools down. This junk pollutes the quality of the oil and would contribute to wear, corrosion and deposits. These fumes have to go somewhere and blowby pressure would expel them under the hood where they might find their way into the cab as well. By the way: the PCV has absolutely NO effect on running performance, ZIP!

 

The EGR system is for the most part passive in operation. It reduces cylinder temperatures thereby reducing NOx formation. If there is some lost power I think it's slight. (more in your head than actually felt) But it is easily disconnected.

 

The air pump is a lot of bother and draws a small amount of power.

 

There is a system to warm carb air during warm up to help with emissions. Once the motor is warm it isn't needed and cool air is best. Having said that, If you are in an area with near freezing temps, rain, freezing rain, and fog, the high humidity and very low temps can cause ice to form inside the carb (carb icing). Warmed air will reduce this and this system should be in place. My '78 had it missing when I got it. I live at sea level and in BC, so lots of rain in the winter. I got a large coffee can and cut it and wrapped it around the manifold with some aluminum auto stove pipe hose to the inlet on the air filter horn and it worked until I could find a proper one.

[datsunaholic]

PCV tubing routing (from the block):

 

 

How it goes to an L16 (non-smog) manifold (L20B manifold is similar, but has the EGR manifold attached):

 

 

Because the prior owner removed the PCV manifold, you lost the attachment point for the PCV. The only way to rectify this is to replace the manifold (probably the entire intake). The PCV function is to burn the crankcase gasses that are produced by blowby and oil dilution/evaporation, which in the olden days was simply vented. The PCV runs it through the engine to be burned, and acts as a stop against backfiring.

 

The tube everyone's talking about on the Weber air filter is the valve cover vent line (goes to the 90 degree angle fitting seen on the 2nd picture). That would have gone to the stock air cleaner as well. That tube is to provide fresh air to the crankcase (which is why it's suppoosed to be filtered) since the PCV is supposed to pull a vacuum.

 

The EGR's purpose is to reduce combustion temperatures by injecting a small amount of exhaust gas (which is inert) into the intake. Reduced combustion temperatures reduce NOx emissions.

 

The Air Injection system (air pump, etc) sends non-inert atmospheric air into the exhaust close to the exhaust valves to help "complete" combustion- basically to attempt to cause more CO to become CO2 by introducing more oxygen.

[copacetickid]

Thanks for those pics d-holic, the first one makes the pcv hose clear to me now. Where it exits the crankcase is totally hidden by the exhaust manifold. My truck is at the muffler shop right now, but when I get it back I'll check to see if the hole is plugged or not (and hopefully not get burned). The '78 manual says that under full throttle/hi-temp circumstances, the blow-by gas can flow backwards through the clean air hose into the filter, so I wonder if that's the only way the blow-by gases are escaping now. Although, the crankcase hole not being plugged would definitely account for the noxious fumes in the cabin. We shall see soon....

 

FUCK. Who would take that off???

 

I'm still thinking of trying to find an adapter and using my stock air cleaner (with the air temp function), but d-holic, you said it won't fit. I'm wondering though, are you using the tall adapter plate? I'm thinking that if I get a short adapter it might give me enough hood clearance to use the existing filter. What do you think?

 

About replacing the pcv hose & valve, I'll have to get one off another truck, but mike do you really think I'll have to get a new manifold? Couldn't I just theoretically scrape off the putty and make a new cover with a hole for the pcv valve?

 

And about the AIS and EGR systems, I have a good grasp on what they do and how they work, but what I'm wondering is how much of a difference they actually make to the exhaust exiting the tail pipe. I.E. would a smog test show significant or negligible differences in pollution levels with vs. without them?

 

I just gotta say d-holic, mike, thank you so much for your help. I can't tell you how much I appreciate it. I wish I could buy you both a beer. Or two or three ;). Message me if you guys ever make it down to Olytown.

[datzenmike]

Thanks for those pics d-holic, the first one makes the pcv hose clear to me now. Where it exits the crankcase is totally hidden by the exhaust manifold. My truck is at the muffler shop right now, but when I get it back I'll check to see if the hole is plugged or not (and hopefully not get burned). The '78 manual says that under full throttle/hi-temp circumstances, the blow-by gas can flow backwards through the clean air hose into the filter, so I wonder if that's the only way the blow-by gases are escaping now. Although, the crankcase hole not being plugged would definitely account for the noxious fumes in the cabin. We shall see soon....

 

FUCK. Who would take that off???

 

I'm still thinking of trying to find an adapter and using my stock air cleaner (with the air temp function), but d-holic, you said it won't fit. I'm wondering though, are you using the tall adapter plate? I'm thinking that if I get a short adapter it might give me enough hood clearance to use the existing filter. What do you think?

 

About replacing the pcv hose & valve, I'll have to get one off another truck, but mike do you really think I'll have to get a new manifold? Couldn't I just theoretically scrape off the putty and make a new cover with a hole for the pcv valve?

 

And about the AIS and EGR systems, I have a good grasp on what they do and how they work, but what I'm wondering is how much of a difference they actually make to the exhaust exiting the tail pipe. I.E. would a smog test show significant or negligible differences in pollution levels with vs. without them?

 

I just gotta say d-holic, mike, thank you so much for your help. I can't tell you how much I appreciate it. I wish I could buy you both a beer. Or two or three ;). Message me if you guys ever make it down to Olytown.

 

If you go to a wrecker there must be lots of them cheaper than trying to make something up. The PCV valve, hose and metal tube into the block would already be on it and easy to hook up to yours. Tell them what you want an give them $10 and you'll take it off.

[copacetickid]

this is what my engine looks like on the right side

 

 

this is the back of the exhaust manifold where you should be able to see the pcv hose if it were there.

 

 

and this is the putty + sheered bolts where the ECs hooked up to the intake manifold (sorry about the quality)

 

[datzenmike]

For warm air you need this sheet metal cover over the exhaust manifold with the pipe on the side. A flexible hose connects to the air filter. Yours looks like it might have rusted off... maybe it was removed?

 

In your second photo, just above the exhaust pipe on the manifold just to the right of the throttle cable you can see where the Tube that supplies the EGR has been sealed off.

 

QUOTE=datzenmike;21602]

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