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Vacuum system help on an L20B Datsun 620


IrvinM

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Hi, I have been trying to hook up my Weber carburetor for the longest now and I can't seem to finish. I think I have solved most of my problems now, the only thing left I think is the vacuum system. I need to connect the valve looking thing on my distributor, and maybe a line on the carburetor and my charcoal canister. By the way, my truck is de-smoged, I have a Weber 32/36 with automatic choke, and a stock L20B engine.

 

I am fairly new to carburetors so help is needed and appreciated.

 

20130830_103058.jpgIn the picture above you can see my distributor and I belive the "vacuum advanvce" (a valve looking thing). I need to connect this some where but I don't know exactly where. I've been reading about it and I will connect it to the only small pipe coming out of my Weber.

 

20130830_100204.jpgThe picture above shows the small and only pipe coming out of my Weber 32/36. It is bronze color and it sits under the automatic choke "solenoid". The one further away is a bolt with a flathead end at the top. The hole in between the two is just a plug.

 

20130829_113241.jpgThis picture above shows a small tube coming out of the intake manifold on the L20B engine, right next to the disconnected vacuum line. The vacuum line belongs to the timing advance from the distributor. My previous stock Hitachi DCH340 carburetor had one of the pipes coming out of the base connected to this small tube. Where can I connect this small nipple to?

20130830_101206.jpgThe picture above shows a small tube coming out of the exhaust manifold. What is it for? I don't recall anything being plugged into this before.

20130829_113300.jpgThe picture above shows my charcoal canister. it has four lines going to it. only one is currently connected; the second one from left to right, or from top to bottom. Hose number one and three are connected together but the final output line goes nowhere. hose number four goes no where as well. What to do?

 

I am sorry for all of the questions but I have no experience with non fuel injected vehicles and/or vacuum systems. Thanks for reading!

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Connect the distributor vacuum advance and the small hose to the charcoal canister to the carb. The line to the canister simply opens the canister so the engine can purge the fumes stored there out a different hose into the intake and burn them.

20130830_100204.jpg

 

The charcoal canister should have the other hoses labeled, but one of them goes to an aluminum tube that goes back to the gas tank vapor vent. Another may go back to the carb to collect fumes from the carb (you now have a weber so this may not now be possible) and there should be another line to the intake to suck the fumes out.

 

 

 

This is the EGR tube but as the EGR valve is gone this is redundant. Trim the pipe about 2 " from the exhaust manifold, crush flat with vice grips and roll the end up to prevent exhaust leaking out.

20130830_101206.jpg

 

 

 

Get this wiring mess cleaned up. Get rid of excess wire and use new connectors. Tape the wires into a neat harness and tie in place on the inner fender. (trust me, I didn't on my 521 and the fan wrapped the ignition wires around it, ripping it off the dizzy) It's worse looking than if all the emissions were connected. Get that return fuel line away from the exhaust manifold. If possible get some metal fuel line and make some nice bends and run it from the pump around the front of the valve cover and under the front of the carb with a bend up and a short length of hose and a pair of clamps to the carb inlet (or outlet) Do the other line the same and zip tie together nice an neat and less chance of something rubbing a hole in it. Way cleaner but mostly... safer.

 

20130830_103058.jpg

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  • 7 months later...
  • 7 years later...
On 8/30/2013 at 1:00 PM, datzenmike said:

Connect the distributor vacuum advance and the small hose to the charcoal canister to the carb. The line to the canister simply opens the canister so the engine can purge the fumes stored there out a different hose into the intake and burn them.

http://2.bp.blogspot.com/-GlY8NGIbH44/UiDXKY3IFkI/AAAAAAAAbQE/MHvCPF9hkps/s1600/20130830_100204.jpg

 

The charcoal canister should have the other hoses labeled, but one of them goes to an aluminum tube that goes back to the gas tank vapor vent. Another may go back to the carb to collect fumes from the carb (you now have a weber so this may not now be possible) and there should be another line to the intake to suck the fumes out.

 

 

 

This is the EGR tube but as the EGR valve is gone this is redundant. Trim the pipe about 2 " from the exhaust manifold, crush flat with vice grips and roll the end up to prevent exhaust leaking out.

http://3.bp.blogspot.com/-Oj0gvMgVdU0/UiDXKahnYGI/AAAAAAAAbQE/mOnY0zCpVAc/s1600/20130830_101206.jpg

 

 

 

Get this wiring mess cleaned up. Get rid of excess wire and use new connectors. Tape the wires into a neat harness and tie in place on the inner fender. (trust me, I didn't on my 521 and the fan wrapped the ignition wires around it, ripping it off the dizzy) It's worse looking than if all the emissions were connected. Get that return fuel line away from the exhaust manifold. If possible get some metal fuel line and make some nice bends and run it from the pump around the front of the valve cover and under the front of the carb with a bend up and a short length of hose and a pair of clamps to the carb inlet (or outlet) Do the other line the same and zip tie together nice an neat and less chance of something rubbing a hole in it. Way cleaner but mostly... safer.

 

http://4.bp.blogspot.com/-7NJEr6hMJW0/UiDXUTB9fSI/AAAAAAAAbQY/LnX7stHx9Lw/s1600/20130830_103058.jpg

Connect distributor directly to carb or connect carb to charcoal canister where labeled “carb” ?and can’t you just cap that little intake hole.

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All distributors since mid 60s have a vacuum port on the side that is used to vary the ignition advance depending on engine load. Heavy load, lower vacuum less advance. Light load higher vacuum, more advance. This vacuum port can also be used as the signal to the canister to purge it's contents. The vacuum opens a valve from the canister to the intake through a small orifice. The intake vacuum sucks the stored fumes from the canister as fresh air enters from below to replace what was taken out.

 

The ported vacuum advance is a small hole in the carburetor just above the throttle plate so at idle it has ambient air pressure and below the plate is intake vacuum. As the throttle is opened the throttle plate swings up to the port and intake vacuum is felt and sent to the distributor. As the throttle opens farther and farther the intake vacuum drops and the advance drops also. By the time the throttle is fully open there is almost zero intake vacuum and zero advance.

 

You could cap it but then your vacuum advance would be defeated along with the charcoal canister. There is a very good reason and advantages for vacuum advance. Most people pull emissions equipment off through ignorance of how it works, what it does and how little the emissions systems actually affect the engine's running. Without knowing how it works, emissions deleting can cause the engine to run poorly by introducing problems that weren't there before.

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  • 2 years later...

About that little nipple in the intake (i am attempting to run a stock carb) would that connect to the tube on the carb closer to the firewall?

The line from the distributor is present and connected to the tube closest to the front while the rear one nearest the firewall had nothing connected, i have read that it was for the egr? but now i am not sure

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There should be two ported vacuum lines on the carburetor base facing the valve cover. The one to the front is for vacuum advance and should connect to the distributor. The second port should have a line to the TVV thermal vacuum valve on the side of the thermostat housing and from there to the BPT and EGR.

 

The 'little nipple in the intake' I don't know what this means or where on the intake. Maybe a picture of it?

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