I am in the process of a complete rebuild of a 1979 400, F-250, including the carb (2150). Local mechanic advised using the least amout of vacuum/emmisions lines (there are no emissions requirements in Idaho). He recommends keeping only:

1. Dist Vac advance (on the driver's side spark port)
2. Choke stove
3. Choke pull-down
4. PCV
5. Evap canister lines
6. That vac line that goes to the aircleaner that works the trap door in there (don't know the real name for it.)
7. Break booster line

Eliminate:
1. EGR
2. Smog pump
3. All ported vaccum switches and delays


So three questions for you all:

1. Is this a good idea?
2. I seem to have 3 evap lines that run down the passenger side of the truck. Where on the carb do these go?
3. Does the vac line that goes to the top of the aircleaner come off the tree just behind the carb (the one that also goes to the break booster)?

Thanks

 

There really isn't any reason to remove EGR. You will see no gains from it. If you do remove it, you will have to recurve the distributor and possibly rejet the carb. It's more trouble than it's worth.

The vacuum line that goes to the air cleaner can come off of the vacuum tree. It can but doesn't have to. It just needs manifold vacuum. It goes to a bimetallic temperature switch on the air cleaner. The other end of the switch goes to the trap door you describe. This is called a hot-air intake system; it is used so that the air intake is diverted to warm air wafted off the exhaust manifold rather than cold outside air during cold temperatures to prevent icing up the carb. Some later model systems have a check valve inline.

Honestly, there really isn't any reason to remove any of the stuff your mechanic told you to do. It's just more work for you. I took the smog pump and related parts out of my '79, only because I installed headers and a new intake and couldn't accomodate the smog equipment anymore.

The three evap lines - one line is actually a fuel vapor hose that goes from the cannister to the carb. If my memory serves me correctly there should be a port for this near the choke tower on the air horn? The second one is a fuel bowl vent hose that runs from the front of the carb (fuel bowl vent valve) down to the cannister. The third one I believe is ported vacuum - most systems I have seen tee off of the EGR vacuum line. You may want to hop on Autozone's website and look up vacuum diagrams for your year truck to be sure.

 

Thanks FMC, I was hoping you'd reply.

So eliminating all of that won't improve gas mileage? I'm not too concerned about power. Take a look at the pics I posted here:

http://wisdomranch.org/shavings-2.htm

I've labeled the carb vaccuum ports as I understand them.

Do I have it right?

The nipple on the EGR valve was crimped off before the rebuild. Could this have contributed to the engine running way rich?

 

Hi there - mileage won't change much by removing EGR. Theoretically, EGR would improve EGR because inert exhaust gas is used to displace fuel\air mixture, so less fuel is used to fill a given volume. However, from talking to others, there doesn't seem to be a noticeable difference. The other smog stuff your mechanic recommended you remove won't affect mileage. One could make the argument that removing the smog pump eliminates some drag on the motor, and while I guess there is some truth to that, I doubt any power or mileage improvements would be noticeable.

The labels on your picture will work fine. You might want to check with a diagram to see if the purge valve vacuum runs through a ported vacuum switch or not, after it leaves the carburetor.

As for the vacuum port of the EGR valve being crimped - it will not cause a rich condition; rather it will cause a lean condition because motors with EGR use smaller jets. When people remove EGR, they find they have to increase the jet size to compensate for the loss of EGR. The EGR valve not functioning would cause a lean condition for your case. Your rich condition would most likely be attributed to a blown power valve, idle mixture screws out too far, float set too high, etc.

 

Great, thanks.

So my third evap line will tee into the egr, and the flow will be back towards the carb.

I'll check the autozone diags also.

Yeah, power valve was a mess. When I took the cover off it was full of gas. So there's my richness.

One more, then I'm done for now. There is a nut with a vac line coming out of it that screws into the intake manifold. It's gold colored, maybe brass? Know what that is? This I could use for the hot air intake sytem, right?

When I got the truck a few years ago the whole vac system was "redneck rigged" (no offense) Stuff everywhere. So I am working from scratch.

 

The line you're talking about sounds like the choke stove; so it sounds like your thinking is correct. If it's a hard tube then that's definitely it. This line threads into the matching threaded port on the choke housing on the carb.

I know what you mean about trucks being rigged up by previous owners. For some reason some people take a problem-free original truck and think they can wire it better, so they rip out everything and do it their "own way," only to find that half the electrical accessories don't work anymore; then the next owner is left with the mess of figuring it out. Luckily we all have FTE. One guy I was talking to on here was saying that the previous owner of his truck redid all the wiring with telephone cord and tape; I can't imagine how awful that was to sort out. When I got ahold of my '79, there was all sorts of emissions hack jobs; someone fabricated a steel block-off plate in between the EGR valve and the spacer plate, vacuum hoses were switched around, or left off completely. Who knows.

 

I'll get a picture of that piece up today. It's not the choke stove (i have all parts accounted for there) . All of the smog pump stuff had already been pulled off and the pump itself was seized so I won't be including that in the vac system.

I found a diagram that shows how the egr/ported vac/vac advance goes together so I think I am good there.

With regard to evap lines. I have two gas tanks. Only the rear one is hooked up. So 2 evap lines (one from each tank) flow towards the carb, and one flows from the carb (the bowl vent) back to the charcoal. Do I have that right?

Thanks again for all the help.

 

Here's the picture, scroll down to the bottom

http://wisdomranch.org/shavings-2.htm

When I took it apart there was a vac line from this to the hot air controller on the air cleaner. Bottom of the pic is front of the engine.

 

Ah, sorry for the confusion. The fitting in the bottom picture looks like a tap for manifold vacuum. It makes sense that it ran to the hot air switch on the air cleaner.

I am sorry but I have not owned a truck with dual tanks so I'm not too clear on how the evap cannister is hooked up in this case, but I would imagine that both tanks go to the cannister and then the cannister purges to the carburetor or air cleaner as you describe. It wouldn't makes sense that only one tank would go and the other wouldn't. Maybe the evap lines from the two tanks are joined in the back of the truck and only one line runs up to the front of the truck? Maybe someone else can chime in here.

Basically, the purpose of the charcoal cannister is to collect evaporative fuel fumes that would otherwise vent into the atmosphere. Any source of fuel is a candidate for this - fuel tank, or the fuel bowl in the carburetor. These fumes of these sources are collected in the cannister, and a purge valve releases these back into the carburetor to be reburned.