I have a 78 f100 and was just wondering about the routing of the vacum lines. I have two off the thermostat housing one goes to the EGR valve and the other goes to a maniflod off the intake at the bottom of the carb. Another line from the bottom of the carb to the distributor and one from the top of the carb to the exhaust manifold. There is another line on the diaphram of the distributor but it is capped off. Just want to make sure the lines are going to the right places. The truck runs alright just seems a little sluggish in the mid rpm band (1200 to 1800).

 

EGR - one line from ported vacuum on the carburetor to the PVS (ported vacuum switch) on the thermostat housing. One more line from the other port on the PVS to the EGR valve. You don't want to run manifold vacuum to the EGR valve which is what it sounds like you have.

Distributor - one line from ported vacuum on the carburetor to the vacuum advance on the distributor. If I'm reading your post right, you have that correct.

Top of the carb to the exhaust manifold - you've got me stumped. Where on the exhaust manifold? No vacuum line runs to the exhaust manifold. Maybe you're talking about the choke stove. Please be more specific.

Not sure what you mean by the diaphragm of the distributor - are you talking about the vacuum advance? I thought you already mentioned that. Unless this is a dual vacuum advance (2-way).

What motor? I assume this is a manual transmission since you didn't mention any modulator lines? No power brakes?

 

In response to your questions, not sure if the line from the top of the carb to the exhaust manifold is vacum or not but it is not the choke stove, that is on the other side of the carb. I looked at the distributor again tonight and I assume now that it is dual vacum advance. The motor is a 300 with a std tranny and no power brakes.

 

Is this line on the very top of the carb? If so, that's an evap. return line. It should come from the evap. cannister on the fenderwell, not the exhaust manifold.

 

I will check that out, I am still looking for some pictures to compare mine to because I think the PO had things really messed up. I won't have time tonight but tomorrow I will post up a pic of my carb for you to have a look at. Also, where should the second vacum line on the dist come from?

 

I will have to dig up some vacuum diagrams. When you post a pic of your carburetor can you also add a picture of your distributor?

 

Pics of my carb and distributor, I hope this clears things up for you.

 

Sorry for the late response. That is definitely a dual port vacuum advance. I searched through all my diagrams, but could not find where the second port originally hooks to. I can't remember where I saw one last. They are pretty uncommon, actually. To tell you the truth though, you can get by without it. In all honesty, it could have been capped like that from the factory as well. It just serves to reduce vacuum advance under certain conditions. As long as you have the one line connected to the front like you have there, you're good. Now, as for where the other end of the line connects to - usually it connects to ported vacuum. From your first picture, it looks like you may have it connected to manifold vacuum (unless there are two vacuum lines with a yellow stripe on your motor, and I'm looking at the wrong one). But, it does look like your vacuum advance is hooked up incorrectly. However, some engines did come like that from the factory, but it isn't as common.

Your hot-air intake system is set up correctly. The line with the red stripe goes from manifold vacuum up to the air cleaner. The only thing you might want to check is that the vacuum motor on the snorkel of the air cleaner is functioning. They have a tendency to rupture over the years, and create a vacuum leak.

The line on the top of your carburetor is definitely the evap. system return, but unfortunately from the picture I can't tell where the line is coming from. But that's the function it should serve. The fitting dumps straight into the air horn of the carburetor.

Looks like you have one large line in the back; I assume that is for your PCV valve. It is usually a 3/8" hose. If that's where it's going, you have it hooked up correctly. I see one more line coming from the vacuum tree on the manifold, it looks like it has a white stripe. I can't really tell where it goes.

Clean looking engine, by the way.

 

Thanks for the help on the vacum lines. I took some of your advice from an earlier post and rerun a couple of the lines. I have run the line from the distributor and put it on at the base of the carb, it was on the manifold before and I ran that line from the manifold to the evap cannister. I capped off the evap line at the top of the carb for now. Also figured out that I have two choke stove lines so I just capped the one off. I drove the truck to work this morning and it seems to be better so I will just drive it for a while and see how it goes. Thanks again for your help.

 

What fmc400 said. At least you have rubber lines and not those hard plastic lines running all over the place...they can be a real canine.