Cleveland Vacuum advance system

[Print Dad 58]

Hello all,

The old guy needs help again. A few friends said my vac advance system is messed up. It could be. It is a 70 351c with stock distributor.

On the vac advance unit there are 2 hoses. The one closest to the distributor cap goes to the port on the Holley Metering block.

The outer hose goes to what looks like a thermal switch to the left of the heater hose. This "thermal device has another line that runs up to the intake manifold. Several people say I should just have one vac line and the others

blocked. I am hoping a friend can help me but I figure this is a great place to find out about 69/70's.

So I need some help. I am attaching a pix

[70Mach03 12]

In 1970 Ford went to a dual diaphragm system on the distributors. The outer vacuum hose is to advance the timing at cruise for fuel economy just like in the previous years (which is good). The closer hose was a vacuum retard line which was for emission purposes at idle (which is bad). Both have to be plugged to set your timing. Many people, including me, would just plug the retard hose and get better performance.

[SlimeGold 69 15]

The way it is now is bass-ackwards IMO. Remove B and C. Plug vacume port that C was connected to on intake or carb base. Move A from current position on distributor to where B was on the distributor. But before you hook A line to B distributor port, reset base timing as described by 70Mach03 (with no vacume at all going to the distributor). Should run and rev alot better once the vacume advance is hooked back up. You can just leave the "thermal device" un- hooked or remove and install a plug.

Edited September 1, 2009 by SlimeGold 69
can't spell for shit

[Print Dad 58]

Hello Slime Gold69 and 70 Mach03,

THanks a million. I was pretty sure she was messed up.

I plan to fix this week. Thanks so much. I hope I can help in the future.

 

Oh yeah...did you guys see my post on the horn.

I am looking at a few wire diagrams and can't find a relay.

 

I stink at electrical worse than vacuum systems but I can't finn a relay

 

Any ideas....I am nervous.Thanks Print Dad

[S code 69 13]

Also make sure the vac advance is hooked up to manifold vacuum and not ported.

[70Mach03 12]

Also make sure the vac advance is hooked up to manifold vacuum and not ported.

 

Yeah, what he said. Ensure you have the outer hose connected for good vacuum at cruise and plug the inner hose for vaccum retard.

 

I actually went to a Crane diaphragm with single advance several years ago. It allows you to use a hex key and restrict or gain more total advance. I run my initial advance timing at around 14 to 16 degrees but limit my total advance to around 32 degrees. That allows it to be more peppy off the line but limits spark knock. With that much initial timing, anything much over 32 degrees total caused it to spark knock. If I could run 100 octane all the time I do 36 to 38 degrees total.

[SlimeGold 69 15]

What are you guys calling manifold vacume and ported? Are you talking about hooking the advance strait to the intake?

Edited September 1, 2009 by SlimeGold 69

[S code 69 13]

Yes, on the older cars before the smogger era the vacuum advance was hooked to manifold vacuum. the ported vacuum started as the emmissions came into play, hook your vac advance anywhere except the ported fitting on your carb, just forget that one exist.

[SlimeGold 69 15]

Ok:huh:.

Edited September 2, 2009 by SlimeGold 69

[bnickel 10,004]

some cars actually work better with the ported vacuum than the manifold vacuum. try both and see which way your car likes it best.

[SlimeGold 69 15]

some cars actually work better with the ported vacuum than the manifold vacuum. try both and see which way your car likes it best.

 

 

That's what I was thinking. To be honest I have never hooked up to manifold vacume. Manifiold vacume would pull full advance at idle. If you have a big cam this may help with idle and performance some, but all of the older engines I have had or worked on run great with ported advance. But he could try both and see.

Edited September 4, 2009 by SlimeGold 69

[S code 69 13]

Ported vacuum makes ne sense on a distributor designed for manifold vacuum, you can run an engine with no vac advance too but that doesn't mean it's a great idea.

 

The logic behind vac manifold vacuum is when you can handle more advance you get it, when you don't want it you don't get it. when do you want more advance? when you're at no load or light load, when do you not want more advance? at WOT and under load. ported vacuum comes off above the throttle plate so it increases as you open the throttle and gives nothing at idle, bad idea, this is why older cars have such low initial timing specs, the manifold vacuum took care of it and allowed for proper advance through the spectrum.

 

Hook it up however it makes you happy, but unless you're running an aftermarket post smogger set up designed for ported you're not doing yourself any favors.

[SlimeGold 69 15]

So where does mechanical advance come in. Does it only come in with engine load or RPM? Vacume advance is only going to pull so much and mechanical will pull the rest up based on rpm, not load. I think it's like bnickle said, manifold vacume may work fine on some and I'm not saying it's not a good idea, but I hook mine up how it works best from experience and how MY car runs.

Edited September 4, 2009 by SlimeGold 69

[S code 69 13]

Yes mechanical advance is only on RPM and that's all you need until your throttle plates start to close and build vacuum.

 

To say some engines run best on ported makes no sense unless it has an aftermarket ignition system intended to run ported, yes it will run on ported or with no vac advance at all but it's not going to run as good as how Ford sent it out the door.

 

Google up the article " timing and vacuum advance 101 " and read it, I don't remember the authors name but he explains it much better than I can. people have hooked thier vac advance up wrong for so long they don't even realize it is wrong, I fought my 440 six pack for years until I figured out I was screwing up and did it right.

[SlimeGold 69 15]

I found it and it's interesting.http://www.bronco.com/cms/node/31 and Here is another opinion on the matter from gofastforless.com.

 

 

 

 

 

 

"You're probably thinking, "Sure there is no manifold vacuum at WOT but aren't I supposed to use ported vacuum for the vacuum advance." Hold onto your hat, THEY ARE THE SAME THING! Except ported is shut off at idle. There are a lot of misconceptions when it comes to the ported vacuum source. After hearing 20 different theories I decided to hook up two vacuum gauges, one to manifold and one to ported, then drive my car and watch it. I found out they are the same, except the ported is shut off when the throttle is closed. Even then I had a hard time convincing guys so I hooked up a couple MAP sensors and a throttle position sensor to a data logger and recorded them while driving then dumped it into a spreadsheet and made a

chart. As you can see, there is a direct relationship between throttle position and vacuum. When the throttle is closed vacuum is high, when the throttle is open vacuum is low, and ported vacuum is the same as manifold except when the throttle is closed. So which one do you want to hook it to? I prefer manifold vacuum. This pulls in more timing at idle which is good since there is virtually no load. Your motor will idle smoother and cooler with the extra timing. One night I was at the drags and my car was running hot in the staging lanes, I swapped the vacuum advance from ported to manifold then it would idle all night at 175°. Believe it or not the purpose of ported vacuum is to raise the temperature at idle, to lower NOx emissions. If you're like most hotrodders that is of no concern to you. If you have a big cam with a choppy idle then a vacuum advance hooked to manifold vacuum can really help. It will idle smoother and requires less throttle to maintain speed. Often a big cam requires you to open the throttle so far that the curb idle adjustment needles won't work. Hooking the vacuum advance to manifold vacuum will allow you to close the throttle some which may be enough for the idle mixture screws to work. Someone told me he noticed less dynamic braking with the vacuum advance hooked to manifold. I didn't notice it on my car but it makes sense. If the motor is running more efficiently with the added advance it will make a less effective brake. So which should you use? Try both and see which you like best".

Edited September 4, 2009 by SlimeGold 69

[S code 69 13]

Right , after the plates open past the port it's all the same. try it, all you have to do is reset your initial and reset your idle speed. if you're having any pinging under load this will help or even solve it if it's not too bad by getting your inital down while still having a decent idle.

[Print Dad 58]

Hello Guys,

I have been watching this thread and trying to learn what to do.

I have done several things. The gas was percolating I am pretty sure.

I could barely touch the front fuel bowl (really hot)

I put on a 1" pheonlic spacer.

I moved the vac line. I am running a line from the side of the metering block to the outside of the advance. I have the vac port on the front of the carb (below bowl) capped.

I have been watching and trying to learn what else to do.

 

I still have a vac line comming of the middle of the manifold to the valve thing on the left of the upper radiator hose. The there is a line from the bottom of that valve to the inner part (retard) of the vac advance unit.

 

I think tomorrow I will cap all the vac lines except the one from the meter block to the advance.

 

When you guys are saying ported and manifold vacuum, I am a bit confused.

I have a port on the front of the carb below the bowl. I also have a vac port on the middle of the intake manifold. Are they the same?

 

THe reason I ask is after i block the retard portion of the advance, I will try vac from the metering block then either of the 2 sources I just mentioned.

 

Last;y...this is a 351 2 barrell heads with a new Holley 600 no float adjustments single pump.

 

I get the car to run pretty good by turning the mixture screws out about 1 and half turns. The car seems to idle pretty well with a tach/dwell.

The problem is when I gently downshift (like coming to a light) the car seems to whant to surge or jump. I am not talking racing or anything just a gentle down shifting.

 

With the mixture screws set for lean..the car seems better but idles poor.

 

I just put on a fuel press regulator, spacer and new in line filter. Haven't driven since, but was hoping to hear the answer to my vac isuues.

 

 

Thanks Jim

[S code 69 13]

Unless you know everything is in good working order I'd just scrap the retard side od the vac advance. then hook the advance side to any vac source that has vac at an idle, this will be anywhere except the ported fitting on your carb, I'm not familiar with that carb but it will be the one with no vac at idle.

 

You can et your idle mixture by ear or with a tach but useing a vaccuum gauge is the best way.

 

Since the crap fuel we have today , your altitude and a bunch of other factors come into play the best way ti time a car is by peak driving it. just go out and at a slow speed floor it and work the engine as hard as you can, if you hear pinging back the distributor of a little at a time until you hardly ever hear it, if you don't hear any ping advance it until you do the back it off a little. after this is established you may need to adjust your idle speed and mix and that should do it. timing is like shoes one size does not fit all, the idea is to run as much advance as you can without going too far, this will get you there if you take the time to figure it out.

[Print Dad 58]

Hello S code 69 and others,

Well today the car has me beaten. I am frustrated.

What I did....

1. - I put on a 1" phenolic spacer.

2. - Replaced the inline clear gas filter.

4. - Disconnected the vacuum on the retard portion. (I capped all the ports)

5. - I ran the vac line to the advance side (front) of distrib vc advance from a line from the manifold. - - - No good

6. - I switched and ran the vac line from the metering block. (This is where Holley says. - - - No good.

 

The carb is about 3 weeks old and is running rich.

What I have tried...gently seated mixture screws, then backed off 1.5 turns. The I adjust for best rpm with tach/dwell and ear.

 

I drive the car, and if I am coasting in first...she lunges or surges.

So I set the mixture screws to 1 full turn out from seated and the car idles a little lower but the surge is not too bad. Even in 3rd, (3 speed) and I am just cruising along at say 40...I feel a lunge in the car.

 

I plan to try and exchange the carb tomorrow. It has never seemed to run right with the carb. Not sure if this will help or not.

 

Just a little more details.

Points, rotor, cap, condensor, wires all new. PLugs new. Autolite 25's.

 

If I can't return the carb...what do I do? Also if I put a carb on and it still does this

what do I do? I did a dry compression and was happy with the #'s. Slight (10lbs) variation in 2 cylinders so I figured i was OK.

 

The motor sounds like it has a cam in it. Not a smooth idle. Not real bad either. With the dwell meter on, it only varies about 10rpms. Not a great steady idle but still pretty good.

 

I need help. I am frustrated. WHat do I do, I want the old girl to run well so i can

move on to rear leafs, front susp etc this winter.

 

Sorry for the long post........Print Dad

[S code 69 13]

It's hard to say since those syptoms can be caused by so many things, but I'd get the timing right first and then see about carburation. lunging is common if you have too much advance, try running win no vac advance at all and see if that makes it better. it can also be from being to rich or too lean, are you 100% sure your choke is opening all the way and that it isn't being sucked back closed a little? this can cause lots of trouble.

 

If you truly are running rich and it's not a choke issue you'll have to jet down to slove it, your idle ports won't do it, I find it hard to think a 2bbl would be jetted that rich out of the box so I doubt that's your problem.

 

Have you checked your total timing all in at the rpm range you're getting the lunging at?

[Print Dad 58]

Hello S code 69,

Thanks for sticking with me. Sorry for the confusion on the thread but the

heads are 2 barrel, the carb is a 600 Holley. I have always run a 600.

 

I am going to try to exchange the carb today, then I will double check timming.

 

I am sure the choke is open, an all ignition parts are new except for for the coil.

 

As far as total timming...I don't really know how to do that.

I can set initial timmming (no vac). When I suck on the advance hose, I see the distributor plate pull inside, so I know it at least moves.

 

I am bummed out. I thought the old girl was pretty close to OK engine wise.

I sprayed cleaner all around and no vac leaks. I am starting to think...valves if it is not

the carb. I was thinking all was Ok because the compression numbers were pretty good (142-152) and not much variation.

 

Thanks again..... Print Dad

[70Mach03 12]

Well just a few random thoughts no real advice. I got rid of points and condensers 20 plus years back and went with a Mallory Unilite system and finally Petronix system on my classic Mustangs. It's a much better spark than the factory single points and helps smooth out the idle and probably helps the power and economy a little too. Also as meantioned above, plug all the vacuum lines and see how it drives. It won't hurt drivability only your mpg at cruise.

 

I'm a firm believer in tuning a carb using a vacuum gauge and adjusting for highest vacuum, a dwell/tach actually does about the same thing. I went to a Holley 670 CFM Street Avenger carb a few years back and it was actually jetted very lean. I went up a few sizes in jets for better drivability.

 

The dwell or point setting effects your initial timing. Stock from the factory calls for 6 degrees initial. I always ran my 302's and 351's at 12 to 16 degrees as long as I could keep the spark knock down. Quality and octane of gas can dictate the amount of initial timing you can run. The total timing also affects spark knock. I use a Crane adjustable diaphragm on my stock Ford distributor which allows me to control the total timing easier and I run about 32 degrees total with 16 initial along with 93 octane gas.

 

As I said no real advice that hadn't already been discussed above just my thoughts. Good luck.

 

My car:

http://rides.mustangmonthly.com/ride/1005705/billhamilton/1970/ford/mustang/index.html

Edited September 6, 2009 by 70Mach03

[Print Dad 58]

Hello 70Mach03,

Thanks for the ideas. I would like to change the distrib but $$ are an issue.

I have had the car over 30 years and just got her on the road after 23 years in the garage. I did a lot of prep work to get her what i thought was right.

I plan to rebuild the front suspension, rear leafs, shocks all around and she needs a paint job (no rust just little chips etc.) So money is tight.

 

I am headed to the parts store to see if I can swap out the carb.

It is so weird.... I should get a vac gauge, but when I set up the carb using my tach and dwell, I get the best rpm at about 2 full turns out from seated. The car idles great (highest rpm), but when I try to drive, she surges. You can feel it especially when coasting. The only way I get it to coast or downshift well is to have the mixture screws about 3/4-1 turn out. I know this could be a lot of things but I don't want to start just replacing without having a pretty good idea of what the trouble is.

 

I am now starting to think valves. Several (6 or more) guys have listened and think the motor is solid. These are long long time mechanics that get together for cruise nights and we talk about the cars and try to help each other out. They know cars. I ask if they think there is a problem inside and they say right away...No. I realize that gthe best way to tell now is probably a vac test.

 

Well thanks for the info. I'll post what happens after I go to the parts store. I have run Holleys for over 35 years and liked the adjustable bowl. I would if I could, check the bowl heights and needle and seat. This new carb has no adjustment and no sight plug for the bowls. i was hesitant to buy it, but wanted to get the car out and try it.

 

Thanks........ Pritn Dad

[Blue70 0]

On 9/5/2009 at 11:32 PM, Print Dad said:

Hello S code 69 and others,

Well today the car has me beaten. I am frustrated.

What I did....

1. - I put on a 1" phenolic spacer.

2. - Replaced the inline clear gas filter.

4. - Disconnected the vacuum on the retard portion. (I capped all the ports)

5. - I ran the vac line to the advance side (front) of distrib vc advance from a line from the manifold. - - - No good

6. - I switched and ran the vac line from the metering block. (This is where Holley says. - - - No good.

 

The carb is about 3 weeks old and is running rich.

What I have tried...gently seated mixture screws, then backed off 1.5 turns. The I adjust for best rpm with tach/dwell and ear.

 

I drive the car, and if I am coasting in first...she lunges or surges.

So I set the mixture screws to 1 full turn out from seated and the car idles a little lower but the surge is not too bad. Even in 3rd, (3 speed) and I am just cruising along at say 40...I feel a lunge in the car.

 

I plan to try and exchange the carb tomorrow. It has never seemed to run right with the carb. Not sure if this will help or not.

 

Just a little more details.

Points, rotor, cap, condensor, wires all new. PLugs new. Autolite 25's.

 

If I can't return the carb...what do I do? Also if I put a carb on and it still does this

what do I do? I did a dry compression and was happy with the #'s. Slight (10lbs) variation in 2 cylinders so I figured i was OK.

 

The motor sounds like it has a cam in it. Not a smooth idle. Not real bad either. With the dwell meter on, it only varies about 10rpms. Not a great steady idle but still pretty good.

 

I need help. I am frustrated. WHat do I do, I want the old girl to run well so i can

move on to rear leafs, front susp etc this winter.

 

Sorry for the long post........Print Dad

I just replaced the leaf springs on my 70 Mach with Eaton Detroit Spring, Inc RB822-138 and now really like the stance.  It sagged before with center eye leafs from previous owner.  Eaton has a great website that walks you through the application/selection.  They're not the cheapest, but the correct spring steel material and leaf clamps.

[barnett468 418]

NEVER EVER use manifold vacuum for vacuum advance on a car that has a centrifugal advance distributor and single port vacuum advance unit, EVER, unless you like having over 30 degrees of advance at idle, so your engine may idle like crap at idle.

Also, ported vacuum has absolutely ZERO to do with emissions.

 

 

.