My vacuum advance went out on my 86 F250, 4x4, 460, C-6, 3:55 gears. So I ordered a new vacuum advance from Napa. Today I picked it up. I noticed it was adjustable. Well, the directions give a setting according to the distributor tag. Well, there lies the problem NO TAG. So I looked at ALL the setting and it seemed that an average was around 3-3.5 turns CCW from stop. That is where I set it. The question is can someone give me advise on fine tuning the vacuum advance, without a TAG#. I have the timing set at 13 degrees with an overall of around 35 degrees. This 460 has the CAM set 4 degrees ADVANCED past TDC. With this I run a high vacuum around 17-19 inches. The Vacuum advance is hooked to ported vacuum. I run an Edebrock Performer manifold, 4160 600 CFM Holley, and 2 1/2" dual exhaust. It is desmoged. Other than that is is stock.

 

There has to be someone here with experience with adjustable vacuum advance. I have never knowingly fooled with it. ANY TIPS?

 

Vacuum advance units should advance timing over mechanical timing 6° to 15° at light throttle settings. Max mechanical advance should be 38° at about 3500 for a truck.

 

You will want to set your initial timing and adjust the vacuum advance to get the total timing that you want.

 

Thanks, I'm right there at 38 degrees so I'm OK it sounds like. I kicked my inital timing to 13 degrees & that seemed to make a positive difference.
Thanks again.

 

vacuum advance is set during a loaded condition. Set it until you get light spark knock while driving up a slight hill in high gear. Then back it off until the spark knock goes away. That should get you pretty close.
clint

 

Never is vacuum advance adjusted or even working at max advance during a loaded condition. Actually while going up that hill is when the vacuum advance drops off and should never be adjusted during that condition. If engine vacuum drops, as when going up a hill, vacuum controlled timing also drops off. It is a gas mileage function for light load conditions while cruising down the highway. As long as it doesn't ping then or cause an overheat it is fine.

 

Go to this link if this site will let you. I have not posted here in ages and there has been a bunch of changes.
http://www.fordmuscle.com/archives/2000/03/timing/
This will explain everything you ever wanted to know about timing, setting up a proper timing curve and setting up you vacuum advance.
clint

 

These low comp 460's like a lot of low rpm advance. I agree with Bear 45/70, vacuum is only an economy feature. I (and my brother) spent an awful lot of time on 460 vans trying to get a good power and economy curve. To do both takes some effort. We got so good at pulling the dist out, we could do that faster than change the radiator cap

What I liked (which is opinion only) was ~ 10 degrees, crank, for easier cranking. You have to set the centrifugal advance to make up the difference between 10 and the 35 degrees. As bear said, set vacuum on top of that for a few degrees that will drop off just as soon as any load is detected (manifold vacuum drop).

You will may have to "shade tree" the slots and springs under the point/trigger plate. What I found that I liked was 10 crank, ~28 centrifugal with ~6-10 vacuum (yes I know 40+ degrees is a lot, but these engines like it under no load low rpm. No, it will not burn holes in the pistons.) I used fast advance springs and got all mechanical in by ~2500-3000 rpm. Been a while, I dont recall exactly.

I suggest check your vacuum guage at a no-load cruise then see what it does under light throttle. Have your vacuum advance in at the cruise vacuum and drop off at light throttle or load. As always, what works for me may not be for you.

 

I agree vacuum advance is an economy thing but it also improves part throttle drive-ability. Adds a lot of crispness to the throttle. At least it does to my truck. Most distributors. that don't have a vacuum canister are meant to be used on race cars that don't spend any time at part throttle.

 

I think all of the after market vacuum advance canisters are now adjustable. Fortunately I have the distributor spec's for my vehicle, so I simply put a calibrated vacuum pump on it and by watching the degrees on the balancer, with the timing light, pumped up the vacuum to the specified In. Hg. That way you can tell how much the thing is advancing at a certain vacuum level. You do this while the engine is idling. That way the centrifugal advance in not put into the equation. You use the Allen wrench to back it down if the degrees are too high and vice versa if the degrees are too low. My particular distributor specifications were 0 degrees at 6 In.Hg. and 28 degrees at 16 In. Hg. It took several adjustments to get it set on spec. The article from Ford Muscle was interesting, but I think trying to set it by driving around is a little troublesome and not too accurate.

 

Since I got me a vacuum pump I do it the same way except I don't have any stock specs. so I am still guessing. The tech link has a lot more info in it besides vacuum advance that could help people understand the whole timing process I think.
Some of the MSD dist. don't have an adjustable vacuum can. but the GM points type dist. vacuum canistor fits some of them.
clint

 

I still like the idea of watching a vacuum guage under driving conditions to verify what the general load on the engine is, then set the vacuum threshhold for the distributor accordingly. No doubt the factory specs are close, but may not account for your personal driving habits.

Whatever works!

 

Thanks for all the good info guys.
Craig