The EVAP system on my truck (carbed 302) originally was electronically controlled by the EEC-IV computer. In converting my truck over to Duraspark II and eliminating the engine computer, all emissions are gone, except for the PCV valve. I would like to hook back up my EVAP emissions controls to cut down on the gas smell.

I have to redo this entire system mechanically, the way it would have been in the late 1970s, early 1980s before engine computers took over. I already have the charcoal canister, an inline canister purge valve, and all associated vacuum lines and check valve from a 1981 F150. I have studied the emissions diagrams in Chilton's for various years, and it seems that FORD routed it differently each year! So that leaves me a little confused on what I should do here.

I know that the gas tank line hooks to an "F" fitting located on top of the charcoal canister to collect the fumes from the gas tank in the canister. The larger, bottom port of this "F" fitting is where a vacuum hose attaches, with the inline canister purge valve located in this line. From the canister purge valve there are three ports:

1. Purge line: One port goes to the smaller top port of the PCV valve with an inline restrictor.

2. Signal line: One port goes to a "VCV" and then from there to an "E" port on the carburetor. What temperature rating should the "VCV" be? My carburetor only has one port on the carburetor, and that is ported vacuum where the vacuum advance hooks to. Can I tee into the vacuum advance line?

3. Carburetor bowl vent line: The larger port on the canister purge valve goes to the bowl vent on the carburetor with a check valve inline, which my (replacement) carburetor does not have. Can I run a line to the air cleaner itself, the way the early 1970s trucks did?

Lastly, when I get this system working, will I have to re-tune my carburetor to allow for the vacuum "leak?"

Have I missed anything?

 

This is what little I know, with some assumptions along with it;

1. What temperature rating should the "VCV" be? I know a lot of them are around 100 degrees, you just need to get the right one. Some open the vacuum at 100 degrees water temp and some close off the vacuum at 100. I would try to find the most simple setup they had, and that's usually the Canadian models by looking at the diagrams at Autozone's site. The engine is a little touchy when it's first started and is warming up. So they don't want to start some of this emissions stuff working till it's warmed up enough to accept whatever they are doing. In this case, they are letting gas fumes enter the intake.

Can I tee into the vacuum advance line? I don't think you have much choice. You probably don't want the system working at idle, or it might cause the engine to run rough.
will I have to re-tune my carburetor to allow for the vacuum "leak?"
Probably not if you use the ported vacuum and the vacuum temp switch, since the system will only be working when the engine is a higher rpm. That being said, I have run across some of these systems where they just plumb the suction line from the canister straight into the intake or PCV valve with no temp switch or anything else. But a lot of these are fuel injected systems, so that might be the difference. But you could try it and see if it works to just mix the canister purge right into the PCV line all the time, and see what happens.

 

Thanks Franklin!

 

With the Carb not being Evap emissions it would be hard to add the system to your truck the right way.

I assume it does not have a port for the EGR either.

Not much more I could tell you that Franklin didnt.

I would look into getting NON-Evap components for the fuel tanks and gas caps, or swapping carbs if it was mine. And swapping carbs I wouldnt really do, especially if it's running well.

EDIT: Adding non-evap components wouldnt help much with the gas smell.

 

I am running a mid 1960s Autolite 4100, and the only port it has is for the vacuum advance. Do you see a problem with running the VCV (opens above 100 degrees) and teeing into the vacuum advance line? This carburetor runs absolutely fantastic on my truck, and I would not want to swap it for something else.

I don't think I would want to go through the trouble of swapping the stock gas tank either. That is why I want to hook the EVAP system back up, at least partially, because right now I have an open hose running from the gas tank to the engine bay with nowhere else to go.

I can plug the gas tank line to the charcoal canister, and then use the canister purge valve to take care of those vapors. The carburetor portion of the EVAP system looks like it is a separate function, so can't I just cap off that part at the canister purge valve?

Compared to the gas tank, does the carburetor contribute much to the gas smell?

Even though the charcoal canister is larger, I noticed that the early 1970s model trucks ran a corrugated hose from the charcoal canister to the air cleaner itself. Could I run a hose from the carburetor portion of the canister purge valve to the air cleaner for the carburetor fumes?

 

Yes the carb can contribute to gas smell and evaporation.

I wouldn't tee into the vacuum advance as it could change your timing curve, but you could try it and see if it works.

You don't have much choice.

What you can do is block the evap line from the top of the tank and get fuel caps from a Non-evap emissions vehicle. The non-evap caps are vented where the Evap fuel caps are pressure relief only if the pressure increase is too great. The only thing you would have to change would be the filler necks to except the new non-evap caps.

Just some more options...

 

I would hook it straight into the PCV line and see what happens.

 

I do not have the EGR anymore, but I do have a 1" carburetor spacer with PVC port attached.

Is the vacuum source for the canister purge valve supposed to be ported or manifold? The vacuum diagrams called for the "E" port, which I assumed was ported vacuum?

 

The canister purge valve is indeed supposed to have ported vacuum to activate, IE: open the other two lines to pass through to each other.