I just bought a 78 F150 with a 351m in it. Runs good except for maybe need carb kit. I was wondering what vacuum lines I NEED and what ones are useless? The line coming form the carb to the Vacuum Advance on the distributor didnt have any vacuum so I ran a line from the vacuum manifold in the middle back by the firewall. I now have good vacuum there....will this work permanantly? Also alot of the other lines are plugged or gone. which other ones are essential?

 

welcome to the site. The vacuum line for the vacuum advance will not have vacuum at a idle, it is timed vacuum. You will need vacuum going to the dash for the heater controls and to the power brakes, if you have them. Can not think if anymore right now.

 

I do believe you should have ported vacuum to the advance , not manifold . Other than that , booster and heater/ac vac supply should be all you "need " .

 

JWC is correct you need ported vacuum to the distributor NOT manifold. If you have the factory air horn on your truck still, then you need vacuum lines to allow the little flap on the end of the snorkel to open and close and a line to go from manifold vacuum to the air cleaner temperature sensor. If you have cruise control you'll need lines for that too. Of course the vacuum line running to the transmission modulator (provided you have an automatic) are essential as well.

Here are the lines I have on my truck:

-Line to the brake booster (power brakes)
-Lines for the air cleaner assembly
-Line to the distributor vacuum advance
-Line(s) for the heater control and AC

Some argue that if you have the old EGR on it and/or charcoal canister on it that you should leave it alone. I removed the egr from my truck and havent had any adverse effects at all (knock on wood!)

 

That makes sense then why I did not have vacuum at idle and I will take it back off the manifold, just thought the vacuum from the carb (ported) wasnt working! So really when they say to take the vacuum advance off and plug it to time it, that is just to be SURE their is no vacuum their? even though at idle their shouldnt be any regaurdless.......

 

Correct just disconnect the vacuum advance when timing it.

 

I forgot the modulator ! Need that for sure , if auto tranny

 

So my factory horn works so that must be hooked up......power brakes work and I did check that vacuum (good).....heater controls work good, so thats good.......um the only one I am not sure about is the AIR CLEANER.......sorry if this sounds stupid but I am pretty green to this, where is the air cleaner located and what does it do?

 

Oh yeah and my Tranny shifts great so that also must have good vacuum....actually I cant believe how good (tight) the tranny is!

 

1. The horn is electrically operated. No vacuum goes to the horn to the best of my knowledge.

2. The air cleaner is the big thing that (if stock) has a big square looking snorkel coming off of it. It sits on top of the carburetor. If you have a 351m in your truck then your factory air cleaner would be the large gray thing in the center of your engine compartment

 

In event you're wondering, the EGR is the thing underneath the carburetor. The charcoal canister (if you have one) should be on the passenger side frame rail in the engine compartment.

 

Ok so if their is no vacuum at idle how will I tell if I have good vacuum at higher speeds? of course their is the obvious, it not running well when you step it down, but do I need to put an inline gauge on it a watch it as I idle it up? Only reason I ask is because it doesnt run well when I kick it down but great otherwise. I was thinking this could be as simple as getting the timing right which I am doing tomorrow, carb adjustment, or VACUUM ADVANCE not good enough (what should I have a 2500rpm?)

 

HOLY CRAP STUPID ME.....yeah I know what that is I just call it the filter not cleaner and thought maybe you were talking about something else. I do not currently have a vacuum from the manifold to the damper on the air cleaner. Do I need this and it should always be under vacuum from the manifold?

 

As far as the EGR.....their is a booster looking thing the size of the bottom of a pop can behind the carb by the firewall that has a plugged vacuum line. Is that the EGR? and what does this do?

 

Holy buckets lotta questions at one time. No problem lemme see if I get get a feel for what youre asking here. Ok...

1. You'll know if your vacuum advance is working at high speeds/RPMS because if it isn't, then your truck will bog and run crappy. Dont worry about this right now.

2. "Kick it down"...what does that mean? I assume accelerate? Or are you referring to "kicking down" the choke at idle? If you ACCELERATE and it runs like crap, many things can cause that. If you open the choke (blip the throttle to drop from high idle to normal idle) and it runs like crap, sounds like a carb adjustment.

3. The inline gauge on the manifold if really only needed for tuning the carb. You dont need it for anything else.

4. At 2500 RPM, you should essentially have little to no vacuum because the throttle blades on the carb are open and air is getting into the engine (Vacuum is the ABSENCE of air...confusing I know )