Some truck applications used a ported vacuum switch located on top of the thermostat housing. This switch is rated at 225F and is used to switch the vacuum advance from the normal ported vacuum to full manifold vacuum when the coolant temperature reaches 225F. The reason being is because at 225F, your vehicle is beginning to overheat. The switch to full manifold vacuum will advance the idle, which will raise the engine's RPMs. That in turn will spin the water pump and engine fan faster to help cool the engine down. When the temperature drops back down below 225F, the vacuum switch switches off full manifold vacuum and returns to ported vacuum.

The mid 1980s carbureted Ford Mustangs used a vacuum switch rated at 130F located at the back of the engine in the intake manifold. This switch is different in that it connects the vacuum advance to full manifold vacuum below 130F and then switches to ported vacuum above 130F. It was done this way to help warm the engine up faster for emissions reasons, but it used ported vacuum under normal conditions. Also, the Mustang used a different carburetor that only used an electric choke, which operates on a timer. These are very inefficient in cold weather, as the choke comes off too soon before the engine is ready. This is good for emissions but not so good with driveability. So the 130F vacuum switch helps with this. In contrast, most trucks used the Motorcraft 2V carburetor that used a thermostatic hot air choke as the primary choke and an electric assist to help the choke come off faster at temperatures only above 60F, so they wouldn't need the 130F switch.

 

Nope. My experience has been putting the dist on intake manifold vacuum dramatically raises the idle speed. Of course this will happen because you are advancing the timing. So then you have to re-adjust your idle speed and usually also the mixture screws need some adjusting also. No problem, and you get it tweaked in and it's idling nicely. Then you go to drop it from park to drive, and then the engine stalls. So you figure out the idle speed is set too low. So you chock the wheels and put the parking brake on, and then set the idle with the tranny in drive, hoping it doesn't run over you in the process. So you get it dialed in again, pat yourself on the back, and you go around and put the tranny in park, and the idle speed of the engine shoots way up. You think to yourself "maybe I can live with that" till you go to put it back in drive, and there is a big bang as the tranny goes in gear, and then you decide to put it back to ported vacuum and re-adjust everything back like it was.

Some vehicles do run manifold vacuum on the dist, as we can see in the diagram above, but they must have the carb calibrated differently, or possibly they have a different milder vacuum advance unit with less advance or a heavier spring in the advance unit.

 

That has been my experience too, Franklin.

 

Oh yeah, I went through some of that too; but in a slightly different way. I idle at right under 500 rpm on the tach regardless of ported or manifold vacuum. It jumps up to 700-800 when put in park. However with ported vacuum, it was worse when the engine was cold; running the idle mixture richer helped. With manifold vacuum I turned down the idle, and it basically acts the same except when cold it improved. Likely because the engine is modified and wants more initial timing.

 

Unrestricted manifold vacuum comes in when the engine starts to overheat.
More vacuum increases the idle speed, and therefore fan and waterpump speed as well, if stuck sitting in traffic.

 

Right, but without the 225F ported vacuum switch, manifold vacuum will not come in when the engine starts to overheat. If the vacuum advance is connected directly to ported vacuum or manifold vacuum only, that is all it will receive.

The 225F ported vacuum switch located on the thermostat housing has three ports: 1, D, 2. This allows the engine to switch between both methods of vacuum advance at different times to suit the engine's needs. The vacuum line from the distributor connects to the center port marked "D." Then another vacuum line connects from the top port "1" on the switch to a ported vacuum source on the carburetor. This is the normal operation of the vacuum advance. Finally, the last vacuum line runs from port "2" to a full manifold vacuum source located at the back of the engine. This line activates only when the "1" vacuum source shuts off and when the temperature reaches 225F.

As you can see, this actually serves a useful purpose. Unfortunately, ported vacuum switches suffer the same fate as the stock thermostatic air cleaner and canister purge valves. I never could figure out why people are so quick to throw these simple devices away.

 

OK i think we are leading to all the theories above related to the behavior that i'm experiencing.

Engine HOT, you start the truck you get a very nice 750 RMP speed, you rev up and off the gas, this time you get 1000 RPM idle speed. Either conditions when you put into drive (D) the engine is able to idle fine, NO stalling.

Cycle the engine to start, again you get a nice 750 RPM speed. How come i have two idle conditions? What does the Start does to cycle to lower RPM?

My water Temp change to also from 3/4 to Max Hot without overheating. This seem to happen right after i put in new fresh full tank of gas. Prior to this, i was still using some old gas from the previous owner. The owner said the truck sits most of his time.
Making me think that the Teflon tape round the Temp sensor sender may not be providing good electrical ground. I measure the engine temp with the handheld laser again 200 deg F. I bought a 180 deg thermostat thinking of trying it.

Timing is set to 10 deg BTDC. Actually the truck drivabilty improved nicely.

XR

 

In post #4 xr-guys states that the VCV is still in place atop the thermostat housing.
The vacuum restriction (VREST) is a simple plastic orifice inserted in the line.
So why not get one and hook it up as it should be?

Mine is blue. I've been told by 81-F-150-Explorer that they are color coded depending on the size of the orifice.
You can see it in front of the top port here.

http://www.flickr.com/photos/24183730@N03/2443360404/http://www.flickr.com/photos/24183730@N03/2443360404/ by http://www.flickr.com/people/24183730@N03/, on Flickr

Seems many people "tear off all that emissions crap" thinking it will help their engine run better or burn less fuel.
And while I'd agree that a pure race engine would produce more power, or an engine can be made that would sip gas, most of the time -if the systems are functioning correctly- all they are doing is hurting both economy and driveability.

 

On the passenger side of the throttle shaft, behind the choke element is a little plastic pawl called the fast idle cam.
Until the choke warms up fully this acts as a secondary throttle stop.
When you first step on the gas it allows this cam to move up and hold the throttle blades open a bit.
With the engine running the electric choke coil spring is energized and heating up like a lightbulb.
It is also drawing a tiny amount of air through the housing due to an internal vacuum port in the carburetor.
When you stop the engine, the coil spring is still hot but the cooling air stops, and it can now uncoil a little more and move to a position that gets the fast idle cam out of the way.

At least this is how I see it.
I may be wrong. I have been before, and will be again.
Perhaps Dave or Lariat know the 4180 better and can explain it to me.

 

That is correct how the choke system works. It should be out of the picture if the engine is warmed up. It is possible though, the choke is out of adjustment or malfunctioning, so he should check to make sure the choke door is straight up and down after the truck is warmed up, and has a little bit of pressure holding it straight up, not flopping around from a straight position to a forward position.

 

Franklin2, that is a correct determination based on what my 86 does. I have advance vacuum at all times, but at one temperature it goes through a restrictor and at others (I don't remember the change point or why) it is direct. The "S" port on the carburetor controls the canister purge valves.

As for the 750 rpm idle on hot start, jumping to 1000 rpm after he taps the gas, sounds like his truck has an idle solenoid like the 351 HO engines used. They typically don't have enough strength to open the throttle by themselves, but require it be opened briefly. Since Ford engines usually will start hot with no throttle, you will see this issue. GM and Chryslers typically need a little gas to start hot.

 

With air conditioning these trucks have a throttle positioner solenoid.
Mine (without A/C) has a simple dashpot to keep the throttle plates from slamming shut and stalling the engine.
Perhaps whichever one of these he has is sticking or mis-adjusted?

 

Jim, mine has factory AC and only has the dashpot.
On yours, the dashpot is strictly for emissions, the anti-stall need is on automatics like mine.

 

... and his, it seems.

Thanks for the insight.

 

Jim,
<O</O
Another good day yesterday, made more progress.
<O</O
Idle Speed issue<O</O
I took your recommendation to use the thermo switch to have two vacuum feeding my vacuum advance on the distributor using the vacuum under the carburetor outlet and the manifold. Also adjust the mechanical decal throttle control, i notice the adjustment screw was max out (pushed closer to the throttle). I back this off around half way of the adjustment (hopping to reduce curb idle speed), in addition to this I also adjusted actual curb idle screw one full turn counter clockwise. Started the truck, NO change, still has two idle conditions. But get this, after buttoning the air filter and started the truck again, it idle 780 rpm then proceed to rev the engine up and walla..! the rpm returned back to 780 RPM. I was thinking it was just a fluke, rev the engine a few more times and start cycle the truck more, consistently the idle was stable 780 RPM. Not sure which one of those adjustments that I did fixed the problem.<O</O

Note:<O</O
By the way according to most pictures I saw on holley 4180c, it should have a vacuum assist type decel throttle control, but mine has the mechanical. Not sure why if the two previous owner this replaced this part.<O</O

Temperature going close to the MAX (H):<O</O
I went ahead and replaced the thermostat to 180 F and pulled the sensor to removed the Teflon tape around it. Refill the water back and went for a test ride. The temperature stayed just little pass the middle marker of the temp gauge, even under hard rolling acceleration and high speed cruising the temperature stayed at the middle. Boy I was happy. I think with the vacuum sorted out this also helped in the cooling issue to.<O</O

Kicker:<O</O
Here is some kicker after all of these success, proceed to clean the engine compartment by degreasing it and added some plastic wring insulations to the wires and tucking them neatly. Started the truck to check for a final button up, after several minutes of warming up suddenly I heard a high pitch noise or whistle coming from the engine. It seems to go away when you rev it up, tried spraying carb cleaning around the carburetor looking for vacuum leak, NO change on the engine during this exercise. After two hours of thinking and scratching head. I went back to check and see if the mounting bolts to the carburetor was tight. Boy I was surprise that they were in fact loose, all 4 of them. By this time its already past 11 PM, decided not to disturb the neighbors. This morning started the truck again to check on the whistling noise and it was gone. That was the issue.<O</O

Note: <O</O
During the thinking down time, i decided to fix the crack plastic mud guard using soldering iron to mender them back, works perfect, zero coast <O</O
Now on to fixing the broken wheel stud. I’m starting to get to know this truck.<O</O

Thanks Jim and everyone for the help.<O></O>