i am new to the forum, i just purchased my 77 f250 highboy. so far im loving it, great truck, great off-roader, perfect for colorado! im just trying to get information on tuning the carb. i bought a vacuum tester but im not really sure where i need to hook it up at to get the best results and what those results should look like. if anyone can help me id really appreciate it. i know vehicles pretty well but this is my first carbed vehicle.
one thing i should probably mention is there is one hose that i can feel a suction through but isnt hooked up to anything. it is the hose on the passenger side rear manifold on the top of the engine. should that be connected somewhere and if so where? i have the 400 in it also. today i went out with the tester and hooked it up to a few spots, only getting about 10 as the reading through either one.

from this website (http://www.cs.utk.edu/~mcdaniel/bronco.html) i think i connected to the maroon and blue hoses. and i think its the green hose that says to air cleaner that isnt hooked to anything, but its a pretty big hose.

i have a rebuild kit for the carb but i wanted to first get an idea of how to tune it and see if itll run a little better without the rebuild since a tune would be a little quicker. the po said it had been rebuilt about 2 years ago and hasnt been driven a whole lot since.

sorry for the novel, just looking for some help so anyone who can point me in the right direction i really appreciate it! i used to own a subaru svx before this and the svx forum like this one was my best friend when it came to stuff i wasnt sure about. i hope this one is just as good!

 

Vacuum gauge goes to manifold vacuum. Any port on the intake or vacuum tree will work fine. A healthy engine will read close to 21 inches of mercury, and the needle should be steady.

Without a picture of your setup, it's hard to tell what the missing hose should go to. My first guess was the air cleaner hot-air intake temperature switch, but again it could be anything. No hose should be unconnected. Try and post a picture with the hoses in question marked.

 

A Quick Online Tutorial --- How to Use and Interpret a Vacuum Gauge

 

hey welcome to the forum. where in colorado? denver here.

 

i live in gunnison. going to school for biology at western state at the moment. ill get pictures posted up with my confusion soon. thanks!

 

That "big hose" you are talking about does go to the air cleaner. It is part of the PCV system, and it should connect to a little black air filter inside the air cleaner assembly.

 

There are quite a few hoses around there; while you're probably right, I'd want to see a picture first before making a call.

 

so i took some pictures and marked the hoses. can anyone tell me how to post pics? anyway, the hose marked red is the one im confused about placement. its kinda hard to see, but it goes into the top of the engine right in the corner where it kind of goes out of view.

the hoses marked yellow are the ones i hooked my vacuum gauge to and was getting a reading of 10. when looking at the tutorial provided it said take off one for every 1000ft in evelvation increase. im at about 8k feet here, would around 10 be a good reading then? if im not hooking the gauge up correctly please let me know also.

another thing i should add is that when the trucks temperature is anything lower than operating temperature, which is around 190 to 220 according to my gauge, it kind of sputters when and is a little sluggish when i get on the gas or in the higher rpms. it runs great once it is warmed up.

thanks for any help! ill have the pics up as soon as i figure out how!

 

figured out how to post the pics so here they are. thanks for any input!

 

In the third picture, it looks like you've got the transmission modulator connected to the carburetor spark port (yellow arrows), which is wrong. Manifold vacuum should go to the modulator. The spark port sources ported vacuum and should go to the distributor vacuum advance. I can't tell where your distributor vacuum advance actually connects (bottom yellow arrow in next-to-last picture). I can't tell where the hose with the red arrow is starting. If it goes to a grommet in the valve cover, then it's probably the breather filter connection. Taping that off will mess up the flow of the PCV system and lead to oil leaks.

Assuming you're measuring vacuum with inches of mercury, 10" is about half of what it should be. As I said before, a healthy engine will idle at close to 21". Either way, none of the places you connected the vacuum gauge to were correct. Connect the gauge to manifold vacuum, which is sourced from the intake manifold.

The hose to your fuel filter looks really pinched in the first picture, but maybe that's just some kind of reflection. I also don't see a fuel filter. It looks like there's another disconnected hose too, but I can't tell where it starts. If you need to take more pictures, please resize them; posting so many large-scale pictures in a single thread makes it hard to navigate.

 

does anyone have a diagram or picture of how it should be hooked up? im a little confused on what needs to be hooked to what. is the diagram i posted earlier a good way to do it? im thinking maybe once i get everything hooked up right and figure out the right place to take the reading the truck will run alot better and be a little better when its cold. sorry about the large pictures, i didnt realize they were that big. thanks for the help!

 

There is 6 pages of vacuum diagrams here. Best I found for now. 400's seem to start on the page in the url. Top line, right side, yellow picture.
Click once to look and a 2nd time to make it bigger. Tough to follow this type of diagram though. I'am curious to, where does that big hoze with the silver tape end up? Need a picture. Thanks a Mil1ion.

Vacuum Diagrams for Ford Trucks pictures from trucks photos on webshots

Jim

 

the hose with the tape just goes into the back pass. corner on the top of the valve cover. cant really seem to get a good picture of it but i can keep trying. the way the light shines through there when the hood is open makes it hard

 

So it could be the hose that would connect into the air cleaner. Just seems long. The intake for the PCV system.

Jim
77 F150 - 400 CI

 

so how exactly should these vacuum hoses be connected if they dont look right in the pictures? i looked at a million diagrams and messed with the routing and the truck is running terribly. at about 55 mph it just cuts out and wont go any faster, usually cutting out until about 45 mph before it will start accelerating again. and where exactly do i hook up the vacuum gauge? i am completely lost here, can anyone help me giving reference to the pictures i posted or another simple method? i really want to learn how to keep this thing running strong and maintained well. it is a beautiful, although old and rough looking mountain machine that i want to be able to count on. thanks for any help!