I own a 78-F150 6 cid stock. I noticed 2 vac ports on the bottom of the Carter 1bbl yesterday. 1 is stamped DIS and the other EGR, both ports are capped and not used. What are they for and should they be utilized?https://www.ford-trucks.com/user_gallery/displaythumbnail.php?&photoid=858&.jpg

 

Dis is for the vacuum advance on the distributer. EGR is exactly what it's for if you're runnning one. Both of these ports are "ported vacuum"

 

There is a third vac takeoff. It is located on the drivers side mid main throttle body. It is not labeled, what is it for?

 

There are different ports for ported vacuum at different throttle positions. There's an extra port on mine I don't use. Did you get the vacuum advance hooked up correctly?

 

Yes, I've switched between the DIS and that extra vac port, and I noticed no diference on how the truck starts or idles? You are saying that the extra port has different vacumm at diferent idle positions?

 

>Yes, I've switched between the DIS and that extra vac port,
>and I noticed no diference on how the truck starts or idles?
>You are saying that the extra port has different vacumm at
>diferent idle positions?

The idea is that at different throttle positions different ports are opened up. They all would have the same amount of amount of vacuum. I have never noticed a throttle difference on mine (Carter YFA)when I checked them out - all three ports seemed to open up above idle - not a 1-2-3 as I expected. If you want a detailed explanation pickup Haynes "Emissions...bla bla" book, it covers the concept.

 

Today I set the timing, and the instructions said that if you remove the vac advance from the distributor that the idle should increase or at least change. I saw no difference when I removed the vac advance from the distributor. I even tried the extra vac port on carb and still no difference. I can almost say, I have no vac advance. The timing is set and the fuel mixture is set, but I saw no vac advance evident. Any suggestions? Truck still has strange characteristics from cold start. Engine goes to high idle fine, then drops slightly and a rougher idle prevails then back to an even idle. The truck goes through several cycles of running fine to dropping in rpms for a short while. Everything conceivable has been replaced, I can't figure her out. When the truck is warm everything is a 100%, thats why I have to figure out this start up problem. If you remove the air cleaner she seems to stay on high idle, but she still fluctuats at different temperatures. This girl has got me beat.

 

> Today I set the timing, and the instructions said that if
>you remove the vac advance from the distributor that the
>idle should increase or at least change. I saw no difference
>when I removed the vac advance from the distributor. I even
>tried the extra vac port on carb and still no difference. I
>can almost say, I have no vac advance. The timing is set and
>the fuel mixture is set, but I saw no vac advance evident.
>Any suggestions? Truck still has strange characteristics
>from cold start. Engine goes to high idle fine, then drops
>slightly and a rougher idle prevails then back to an even
>idle. The truck goes through several cycles of running fine
>to dropping in rpms for a short while. Everything
>conceivable has been replaced, I can't figure her out. When
>the truck is warm everything is a 100%, thats why I have to
>figure out this start up problem. If you remove the air
>cleaner she seems to stay on high idle, but she still
>fluctuats at different temperatures. This girl has got me
>beat.

An easy way I've been able to test the Vac. advance is to pull a vacuum (using vacuum pump) on the vacuum advance line (going to dist.) and carefully note how the timing "advances" with a timing light. The vacuum advance only "works" when there's a vacuum signal going to it - that's when the ported vacuum (off the carb) open up. To set the curb idle, I pull and plug the vacuum advance line, securely set the parking brake, put in drive (AT), and carefully adjust the rpm to 550 (on the VECI label). In doing so, there's always a noticable difference in RPM's when the truck in park and in drive at a stop. It sounds like you may have a vacuum leak present when cold (possibly due to a pollution control device not being engaged untill she's warm) or the choke isn't openening up soon enough - litterally suffocating her - my guess is a vacuum leak, does she hestitate when you punch the gas when cold?

 

No, there is not hesitation in the pedal. By setting the fuel mixer properly I eliminated any hesitation. I am pretty sure I don't have a vac leak. The thermo spring on the choke assembly is new, and I have her leaned out past any lean marks, because the choke butterfly chokes to much. I have read that others on the forum have been experiencing the same cold start characteristics. I've read stories about shortening the thermo spring to bending the linkage for the fast idle cam. I don't know what to think anymore. My next move is a rebuilt carb,maybe that will solve my problems. If that doesn't work, then I will assume that because of an older carburated truck with a few miles on her that this problem is inherent. Thanx for following up with me in previous posts.


Boomer