vacuum advance question

Spanky · Post by **Spanky** » May 26, 2011, 7:40 pm

Why does my 223 run better with my vacuum advance unplugged?
With the line disconnected, it doesn't misfire anymore...
Shouldn't it run worse?
Thanks, Mike

ezernut9mm · Post by **ezernut9mm** » May 26, 2011, 8:40 pm

sounds like the spark control valve is bad maybe? is it an autolite or holley?

Spanky · Post by **Spanky** » May 26, 2011, 9:08 pm

It's an autolite. I just rebuilt the carb because it was leaking fuel very badly now it's fine but just trying to tweak out the carb and the timing. I had to diconnect the vacuum line to turn the distributer (hard line) and got it sounding ok with the carb and the turning of the distributer and connected the vacuum line and right away sounded terrible and really rough like it wanted to die. So I disonnected it and took it around the block a few times and it ran fine. ?? So this is where i got stuck. do I have to hook it back up? And is it bad to run the engine with it disconnected?

Hoofbeat Racer · Post by **Hoofbeat Racer** » May 26, 2011, 10:39 pm

Best article I ever read about vacuum advance

http://www.460ford.com/forum/showthread.php?t=117504

charliemccraney · Post by **charliemccraney** » May 27, 2011, 7:15 am

Are the vacuum lines hooked to the same locations? Do you remember where the distributor was before you changed it? If so, put it back. If not, get a timing light and set it to the recommended spec. Is the problem fixed? If not, then the only other thing you changed is the carb. Figure out what about the carb is causing this - assuming of course that you did not have this symptom before rebuilding the carb.

Spanky · Post by **Spanky** » May 27, 2011, 9:32 pm

well, today I got a timing light and a vacuum gauge. I got it timed right at 4 degrees as per the shop manual. popped on the vacuum gauge and it's holding steady right at 5! It says I have a massive leak somewhere. I did replace the manifold gasket and sealed it good and checked the bolts are all tight. However, I have the line hooked to the carb and not the manifold. I see a plug on the mainfold I guess I need to try and try to find some sort of fitting to plug the vacuum gauge into the intake manifold??? Is that a better place to check the vacuum? right on the manifold verses the carb?

charliemccraney · Post by **charliemccraney** » May 27, 2011, 9:54 pm

Manifold vacuum is what you have to measure to determine if you have a vacuum leak. Some carbs have ports for manifold vacuum. I don't know if yours does or not.

ezernut9mm · Post by **ezernut9mm** » May 27, 2011, 11:28 pm

yes. go to the hardware store with one of those plugs and buy a brass fitting with the same thread pitch/size and that is barbed on the other end for the rubber line from your vacuum gauge to fit with.

cdherman · Post by **cdherman** » May 28, 2011, 8:59 am

Spanky wrote:well, today I got a timing light and a vacuum gauge. I got it timed right at 4 degrees as per the shop manual. popped on the vacuum gauge and it's holding steady right at 5! It says I have a massive leak somewhere. I did replace the manifold gasket and sealed it good and checked the bolts are all tight. However, I have the line hooked to the carb and not the manifold. I see a plug on the mainfold I guess I need to try and try to find some sort of fitting to plug the vacuum gauge into the intake manifold??? Is that a better place to check the vacuum? right on the manifold verses the carb?

You are going down the wrong path worrying about manifold vacuum. While, you might have a vacuum leak somewhere, it certainly would not explain why hooking up the vacuum line to the dizzy makes your engine run WORSE.

Here's what I know vacuum advance and 1100/1101s (and I know a lot about 1100/1101 carbs).

1) Autolite 1100/1101 came in two flavors, those with spark advance and those without. Those with a spark advance valve sticking out the pasenger side of the carb have some complicated internal passages and actually supplies a lower initial vacuum to the dizzy. But what the spark advance valve does is switch over to venturi vacuum, which actually exceeds manifold and throttle body vacuum when you are WOT (wide open throttle).

2) This spark advance system was an attempt to fix the problem that vacuum only advance falls off at WOT, but you still need advance. It has to be paired to a special distributer that has NO mechanical advance and just vacuum. It uses lower levels of vacuum as well to achieve the same degree of advance. Together the system was called "loadomatic" -- note that specifically under load at WOT is where this system was useful.

3) Later, mechanical advances become more popular. In 65, the 240 engine got an 1101 with Loadomatic and the 300 got a conventional distributor with mechanical (contrifugal) advance and vacuum. By 66, loadomatic was dead at FoMoCo. The later style are called dual advance. The 1101 carb lost the spark advance valve and did not have the complicated passages. The vacuum port supplies "ported" vacuum to the distributor, which is to say that there is a port, ABOVE the throttle plate. At WOT, the manifold and ported vacuum are the same, but when the throttle plate is closed or partially open, the vacuum from the port is lower than from manifold.

If you have a loadomatic distributor, you really need to run it with a carb with a functional spark control valve.

Now, to the concrete:
-- do you have a spark control valve?
-- did you replace it?
-- plug your vacuum guage into the vacuum port on the carb (passenger side) At idle it should be very low, less than 5. Then as you open the throttle, the vacuum should rise, hopefully to around 15-18. If you were to get fancy, and have long enough vacuum line, you can run a line into the cab and do this same test out on the road. In this case, the test will vary, depending on if you have a functional spark advance valve or not. If you have a conventional (no spark advance) carb, you will see at WOT under load on the road, that the vacuum falls off. With loadomatic, the valve should switch over to vernturi vacuum and the vacuum will stay up.
-- try to rotate the rotor on the distributor. Does it turn about 30 degrees and then spring back when you let it go? If so, its a dual advance dist. If it does not, then its a loadomatic vacuum only dizzy.

In the end, timing to the marks on a 50 year old engine may run you into trouble as well -- many of the harmonic dampers have spun some through the years. But in any case, you should set the initial advance with the vacuum line disconnnected from the distributor AND plugged. Once its running smoothly at idle, then reconnect the vacuum. If you are connected to manifold vacuum, it will run rough, but ported vacuum should not do anything at this point.

Spanky · Post by **Spanky** » May 28, 2011, 9:54 pm

cdherman -
WOW! Thanks for the help! Lets see.. Yes, I do have a spark control valve and I did replace it. I did plug the vaccum line into the carb and as you said it was reading at 5. However, I dont know what it was giving it gas because at the time I didnt know to do that. I just now saw your post but earlier I was out working on it and before I came inside. what I did was check vacuum at the intake manifold and heres what happened,
-with the vacuum line off:
choke out holding at 18
choke in holding between 16/17
-with vacuum line on it started holding around17/18
(one note too was I reaplaced the hard vacuum line with a rubber one with clamps on either end. old one cracked?)

I made sure everthing was tightend down good and let it warm up some then checked the idle setting. It still seems just a tad rough not to bad though. I realize its an old truck.

Does it sound ok then? Thanks so much for all the info on this carb! I really appreciate it.

Spanky · Post by **Spanky** » May 28, 2011, 9:57 pm

ezernut9mm wrote:yes. go to the hardware store with one of those plugs and buy a brass fitting with the same thread pitch/size and that is barbed on the other end for the rubber line from your vacuum gauge to fit with.

I did exactly that! thanks for the tip!

cdherman · Post by **cdherman** » May 28, 2011, 10:07 pm

Sounds like you have decent vacuum at idle. But even a small leak may be causeing the engine to run really lean at idle. That extra air getting in causes a "lean" (too little gas) condition.

But your original observations of it running OK with the vacuum advance disconnected and then running poorly when connected do not support a major leak.

I think 5 in of vacuum off the carb at idle is too much. Assuming you have a funcional loadomatic distributor (did you check the rotor for "spring" and I descibed?), that 5 in of vacuum will probably be advancing the timing even at idle, which is not really what is supposed to happen.

When you set the timing, I assume you set it with the vacuum detached, and plugged? Did you measure the timing after you reattached the vacuum?

It just strikes me that your vacuum is too high at idle. When you rebuilt the carb, did you check the throttle plate for proper position? Usually the rebuild instructions will give measurement, often stated as the size of a numerical drill bit, that the throttle plate is supposed to be "cracked open" to at idle. If the throttle plate is too open at idle, this *might* cause the ported carb vacuum to be too high. I would check that....

Spanky · Post by **Spanky** » May 29, 2011, 10:02 am

Ok, I did the spring test and figure it's a loadomatic. It did not move when I tried to turn it. After I reattached the vacuum line I rechecked the timing and it was advanced by a good bit, so I turned it down some and it did seem to help. I had some help from a coworker rebuilding the carb being it's the first time I've ever messed with one in my life. So, I will ask him to see if he remembers how he set it. Or can I just let it idle and look at the throttle plate to check the position? And while I'm looking at it's idle postion I'm assuming it's while the choke lever is pushed all the way in? Thanks again, Mike

cdherman · Post by **cdherman** » May 29, 2011, 6:03 pm

You cannot check the throttle plate position with the carb on the truck. You have to check it from below.

How did you set the idle screw? IIRC, the instructions are to screw the idle screw all the way in and then back it out 2 turns. Better verify that I am correct on that be.

If that is not set correctly, then you may have had to crack the throttle adjustment screw too far open to get it to idle. That might in turn cause the higher than expected vacuum, but maybe not....

What idle RPN are you running?

Anyhow -- its a challenge getting these old girls to run, but its rewarding when you get there....

Spanky · Post by **Spanky** » May 29, 2011, 9:07 pm

I did check the idle screw about two turns out. With everything hooked up I checked the RPMs with the timing light and it was saying at idle 1480-1500 range. Seems to run better timed at 8 degrees instead of 4 degrees though. at least at idle. I took her on a test drive just now around the block (in case I had to push it home needed to stay close! hehe) anyways it doesnt run very good at all like something holding it back (kind of bogging down, no enough to die though.) So next step is off with the carb like you suggested to check the throttle plate position. Wow this is kinda frustrating. I have faith though she'll be purring along soon enough though!

cdherman · Post by **cdherman** » May 29, 2011, 9:52 pm

Idle at 1500? Too high. That could be part of the problem. Are you needing to set the idle that high or it dies?

Rebuilding an 1100 carb never was very easy for me either. I finally ended up getting one from Ponycarbs that ran well. But none of them ran as well as my Carter YFs.

But with the loadomatic dizzy, you should not give up on the 1100 just yet.

I would take it off and get the instructions back out on the kit that you used to rebuild it. Run through the settings again, step by step, and see what you have.

That idle of 1500 is either the cause, or a symptom of something else.

If you cannot get it to idle at less than 1500, then then perhaps the concerns that were raised earlier are correct -- a vacuum leak will do that.

But I would check out the carb first and then pursue a possible vac leak only after you are more sure the carb is set right.

Good luck, Hang in there. The old 1 bbl carbs can be made to run quite nicely, but it require patience and some luck too...

66fordtrucknut · Post by **66fordtrucknut** » May 30, 2011, 5:19 am

I have a single barrel Holley on my 223, i had to advance the timing a little too to make it run right, I was told it's because of the crappy gas now a days and alot of people are doing that. it should idle at going by memory only something like 450 rpm, Good luck with it.
Charlie

66fordtrucknut · Post by **66fordtrucknut** » May 30, 2011, 8:04 am

You got me thinking a little, mine has been idleing a rough this year since she came out of hibernation and smelling a little rich, mine won't run worth a crap under 8 degrees, thats where it was set before, tried fooling with it again no luck back to 8. Idles best at 475-500, readjusted the idle mixture, took it out for a little test, ran great idle smoothed out and the rich smell went away. I went thru the same thing 6 yrs. ago when I 1st bought my truck. had the carb off off a 1/2 dozen times. You'll figure it out.
Charlie