73 Vacuum Advance

Hey everybody; new to the forum. I've got a '73 Bronco (302) in...less than steller condition, which i've been (slowly) building back up to be road worthy. Mosty recently i've been trying to firm up the various loose wires and hoses hanging everywhere. What's got me scratching my head the is vacuum advance on the distrubutor: As it stands now, there are two lines going into the diaphram on the distrubutor; one goes directly into the carb, and the other goes into an odd looking cynider with a cap mounted on a bracker on the passenger side behind the carb. Another hose goes from the odd looking device into a small metal square bolted into the top of the block directly behind the carb. Another hose from there is hanging loose and has a bolt stuffed into it ?:?
There is also the stange electrical switch mounted behind the drivers door jam (a distrubtor advance/temperture/low gear thing?); one wire end has a lug thats not screwed down anywhere and the other end got traced into the engine compartment that hangs loose. Another wire goes from a lug on the transmission into the engine compartment and is hanging loose next to the other wire.

I've been racking with this for awhile now, and can't figure out where everything is supposed to get wired up to. If theres an electrical switch for a vacuum advance, there should be a solenoid somewhere, right? If anybody has any insight into what this strange stuff is, how it gets hooked up, and maybe even what i'm missing, please let me know. What I don't know about 1970's emissions and carbeurators could fill a wharehouse.

alan

Welcome!
You have a dual diaphram dist. They are not very good sounds like the previous owner unhooked the retard part of the diaphram which most people do. Makes the engine run much better. Unless you need to keep all your emmissions equip for emmissions test I would leave as is or remove and block any open vacuum sources.
Just remove the switch and wires behind the door jam sounds the the PO had something jerry rigged up and removed what ever was there but left the switch and wires its definitly not stock.

So the dist has a vaccum advance (the line straight from the dist to the carb), and ALSO a vacuum retard (the lines from the other stuff)? Please excuse my ignorance, but I know sh*t about this stuff; Why would you need to retard the timing based on the vaccum? The engine is never going to need to run at a lower RPM than the idle, which is 0 vacuum once it evens out, and no advance? You can't really have a 'negative' vaccum (boost?) on a stock engine, can you? What was the main objective of all that crap? Again, thanks for educating me ?:?
alan

The outer most port (advance port) on the distributor pulls the timing plate into an advanced timing condition. The top/rear port (retard port) on the distributor pulls the timing plate in the opposite direction. The advance port is hooked up above the butterflys on the carb. This provides vacuum when the throttle opens. The retard port connects to full vacuum, hooks up to manifold vacuum. This draws the most at a closed throttle condition.

Herev you go

The purpose of the retard section is to reduce emmissions by retarding the ignition. I have the same thing on my 71 and when I hook it up it runs crappy unhooked it runs pretty good.

Hey, thanks everybody for the replies, but (of course) I still have a couple questions: On the diagram, the retard vacuum line is T-eed into a line that goes the 'Air Bypass Valve'; I've looked high and low in the engine compartment, and can't seem to find it, anybody have a clue where it could be? I think the PO put the power-steering in aftermarket, so it might of gotten removed....
Also, a little searching came up with the following phrase: "The advance is cut off above certain tempertures when the transmission is in low gear". Is their a solenoid (Air Bypass Valve?) controlled by the switches on the MTX and the Door Jamb? I've never even heard of 'vacuum retard' before, is it more of a 'advance cut off'?
The way the diagram shows, when the carb vaccum opens the control valve, wouldn't the advance and the retard both be equal to the manifold vacuum, cancelling each other out? ?:?

thanks for putting up with my dumbass

broncnaz said:

The purpose of the retard section is to reduce emmissions by retarding the ignition. I have the same thing on my 71 and when I hook it up it runs crappy unhooked it runs pretty good.

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Thats funny , Mine runs better with the stuff on there, I just looked and found out how to adjust it all

feitctaj said:

Thats funny , Mine runs better with the stuff on there, I just looked and found out how to adjust it all

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I havent bothered to try and time it correctly for the setup and my air bypass valve is not hooked up correct according to the diagram so that could be why it runs like crap
Quote
jkimmel8
Also, a little searching came up with the following phrase: "The advance is cut off above certain tempertures when the transmission is in low gear". Is their a solenoid (Air Bypass Valve?) controlled by the switches on the MTX and the Door Jamb? I've never even heard of 'vacuum retard' before, is it more of a 'advance cut off'?
The way the diagram shows, when the carb vaccum opens the control valve, wouldn't the advance and the retard both be equal to the manifold vacuum, cancelling each other out?
No switches involved in this. At least not electrical anyways. Its kinda like you say that the retard cancels the advance but its all timed with Vacuum but the advance side doesnt really advance that much at low speed becuase the vaccum to the advance side is ported the carb butterflies have to be opened up a certain amount before the advance kicks in while the mechanical advance is starting to come into play and the engine vacuum is high the retard section retards it to reduce emmissions. Dont know if this actually explains it better or not but it works if everything is right otherwise its a whole lot of tubes and clutter. its more of a PITA than its worht most of the time. I'll have to look at my 71 again but I'm pretty sure that it doesnt have a temp switch on it.

I do not understand where you are getting the idea that the Retard stuff or whever you called it , does not work.
The real name for it is Deceleration Valve, It does nothing but stop the Pop Pop Pop out the tail pipe under deceleration.
the other one you are refering to is Called a ported vacuum switch, it is there on later ones , for to raise the engine RPM when the engine temp raises too high.
It is great to keep it from over heating, I have both on mine with dual vacuum dist, and when it gets too hot it retards the motor and raises the RPMs and cools the motor at The long jack in the BOX line

I have no doubt that when working it does its intended purpose reduce emmissions. Almost all the vehicles I've owned that had this system on them ran way better with it removed. Cant say I noticed and differance in the engine temps but I wasnt looking for it and never had any cooling issues. Of couse most of my engines dont stay stock for long and The dual diaphram does little for performance. It makes little sense to me to bump your timing up intially just to knock it back down again with the retard. My 71 has no temp sensing device on it like the 73 had. the thermostat housing is not even drilled for it. So I'm a little lost on its function on my 71 but I will investagate because I'd like to see how its supposed to work maybe the PO replaced the thermostat housing with one that doesnt have the switch but other than spark plugs, fuel pump,t stat and water pump I dont believe the my engine has been touched since it left the factory.
I fully understand its use on some vehicles like the 302 boss with automatic trannys as the Boss was over cammed and didnt like to idle down low so the retard portion had its use there. And vehicles that are dead stock probalby do run decent with this setup as the factory basically put combos together that would run in a varity of conditions so carbs were usually setup to run on the rich side and to correct this problem it was easier to throw a few hoses and switches to play with the timing than it was to tune each carb to the engine. The popping in the exhaust is more of a rich condition in the carb than it is timing although timing can cause or get rid of it so can a properly tuned carb. I've run single diaphram and straight mechanical dist's that didnt cause popping in the exhaust unless the carb was out of tune.

if there's no electrical involved in any of this, what do the two mystery switches go to? The one mounted inside the door has it's contacts closed at normal atmosphere temp, but opened when it gets cold (sticking it in the freezer proved this). The one mounted in the tranny is closed in 1st, 2nd, R, and N, but not in 3rd. both of these wires ran into the same harness, ran into the engine compartment, across the drivers side vavle covers, and were dangling free towards the Driver side of the distrubutor. Pending any other explainations, the one here seems like the best one. But if that's the case, then i'm missing a solenoid somewhere....

Looks like thats what your talking about. I've never seen that setup Maybe its a California emmisions thing as they had the most emmission crap put on them to satisfy the stricter laws there.
You may have had a soliniod on the carb that would open the throttle blades at a certain temp. personnaly I wouldnt bother with that stuff unless the DMV is hasseling you about it which I doubt they would they are usually only looking for smog pumps and cats, I'd remove it and most of the other unessesary wires and tubes and just run the advance side of the dist. I would guess that it may cost more money to try and get this system working again that it is worth.