View Full Version : Running better w/o vacuum hooked to distributor?


Dave_in_Texas
05/05/10, 09:53 PM
I'm still troubleshooting why my Bronco isn't running too well. The complete history can be found in this thread (http://classicbroncos.com/forums/showthread.php?t=155694). My question right now: Why does my Bronco run/drive much better (not great, though) when I disconnect the vacuum hose from my distributor? Is this an indication that my vacuum advance needs adjustment? I know very little about distributors, so any advice is welcome.

I did pull a plug and look at it. They are still pretty new, but looked slightly gray-ish in the middle and a small section on the outer rim a little white-ish.

Dave

broncnaz
05/05/10, 10:23 PM
By runs a little better what do you mean? just overall way it runs or better idle? It could be that the vaccum advance diaphram is ruptured and is/was cuasing a vaccum leak which would cause a lean condition ie the white/ greyish plugs.

Dave_in_Texas
05/05/10, 10:32 PM
Good question. By running better, I mean it doesn't stumble as much as compared with it plugged in. With it plugged in, I really have to ease the clutch out. With it unplugged, there is less effort in keeping it from dying. No other changes other than unhooking the vacuum advance line AND plugging it.

The idle drops quite a bit with it unplugged though...not enough to kill it, but certainly a decrease. One other variable...I do get a small bit of popping in the exhaust when I drive it w/o vacuum advance.

How would I test a vacuum advance diaphragm to see if its good? If that could cause a vacuum leak somehow then it would explain why it feels lean when under load (accelerating).

Dave

PS-I believe I have full manifold vacuum, as I get lots of suction at idle.

broncnaz
05/05/10, 11:05 PM
Yep you have it hooked to the wrong port if it has constant vaccum at idle.
One way to test the vaccum advance diaphram is to remove the dist cap then you should be able to move the breaker plate towards the advance canister once it stops put your finger over the nipple on the canister and let go of the breaker plate it should stay in postion if it moves fast or slowly back then your diaphram is bad.(also long as your sure your finger is sealing the nipple good)
If you were hooked up to constant vaccum at idle what is your timing set at? How are you setting the timing? I have a feeling that your diaphram is good but your timing is retarded to far as once you step on the gas vacuum goes away as does all the advance given by the vaccum and will cause a bog or hesitation due to it being retarded which will also cause poping in the exhuast as the spark is not burning all the gas so it gets into the exhuast and pops.

Dave_in_Texas
05/06/10, 07:43 AM
To answer your questions, I use my vacuum gauge to set the timing for the highest possible vacuum (20 hg with the gauge hooked up to the hose running from the carb to the vacuum advance). However, when I check this with my timing gun, it looks to be set at 25 degrees (distributor nipple is pointing towards the passenger front headlight)...which seems really high.

The vacuume advance is plugged into the passenger side (towards the bottom) of the carburator and I do get constant vacuum at idle. If this is the wrong spot for it to be hooked up (this is how the PO had it set up), where should it come from?

I'll test the vacuum advance later tonight.

Dave

RangerRob
05/06/10, 08:05 AM
Not sure what carb you have but conventional wisdom (on Ford's at least) is to use PORTED VACUUM for the dizzy advance. Sounds as though yours is set up for constant vacuum, which would cause the problems you are having.

Look for the ported vacuum source on your carb and connect to that. You might have to reset your base timing, but I think it will put you on the right track.

LockedupXJ
05/06/10, 08:06 AM
To answer your questions, I use my vacuum gauge to set the timing for the highest possible vacuum (20 hg with the gauge hooked up to the hose running from the carb to the vacuum advance). However, when I check this with my timing gun, it looks to be set at 25 degrees (distributor nipple is pointing towards the passenger front headlight)...which seems really high.

The vacuume advance is plugged into the passenger side (towards the bottom) of the carburator and I do get constant vacuum at idle. If this is the wrong spot for it to be hooked up (this is how the PO had it set up), where should it come from?

I'll test the vacuum advance later tonight.

Dave


There shouldnt be constant vaccum going to the distributor, it should be hooked to ported vaccum, that would only allow the advance to work when the throttle is pressed. The way you have it now is giving you full advance on the distrubutor at idle.

broncnaz
05/06/10, 08:13 AM
I believe it should be hooked up to the port coming out the front of the carb. 25 degrees timing at idle is to high you should only be at around 6-12 without the vacuum hooked up. The vacuum advance is probably accounting for about 20 degrees by itself so as soon as the throttle is open you lose all your timing.

Dave_in_Texas
05/06/10, 08:46 AM
Guys-

Thanks for all the tips. I'm a little confused, so please bear with me.

I did a Google search and found an image (http://www.allfordmustangs.com/forums/attachments/classic-tech/57885d1230766515-2100-carb-diagram-fittings.jpg)that may explain what I have. This is not my carb, but an illutration of where my vacuum advance is hooked up...see the RED arrow. If memory serves me correctly, I don't have an outlet to connect to on the front. Mine looks similar to this photo (https://www.fordmuscle.com/forums/attachments/mustang-pages-1965-1973/4291d1213864639-quick-carb-help-autolite-2100-2150-idle-mixture-adj_2.jpg).

It is from this tube (the red arrow) that I get 20 hgs at idle...pretty good suction. It is below the throttle plates, so that IS full vacuum, correct? I don't see where else the advance could be hooked up...but will try anything!

Dave

PS-FYI...since I have a manual choke, I don't have anything related to the green arrows.

broncnaz
05/06/10, 09:06 AM
Yeah if your getting vacuum at idel that is a full vacuum port. Try leaving the vacuum advance unhooked and set your timing to spec then see how it drives. You'll probably need to reset your idle mixture screws to get a good idle. the vacuum advance is not required it just makes part throttle operation a little better.
I'm going to go look through my pile of 2100 carbs see if I have anything to you have. I'll get back to you.

Scrapper_MV
05/06/10, 09:27 AM
I just went through this. My engine had a hesitation that I just lived with for the last year. I recently had the distributor out for an unrelated reason. When I was putting it back in and setting the timing I noticed that disconnecting the vacuum advance caused the idle to drop. It almost stalled. So I checked the vacuum at the carb and it was full manifold pressure. I moved the vacuum advance hose to a ported fitting (no vacuum at idle) and reset my base timing.

Not only is the hesitation gone, but I have amazing throttle response. My engine can now easily spin the tires right off idle! And cold starts are much easier, it runs much better when its cold. I cant wait to go wheeling, I think it will be much better off road now. What a difference moving that little hose made!

I could have never figured this out on my own, I had to call Bronco Ben (73Stallion) 3 times to help me figure it out. Thanks Ben!

bmc69
05/06/10, 09:36 AM
What Scrapper figured out and fixed is exactly what you have to do. The dizzy cannot be connected to a manifold vacuum port..never. IT must be connected to the correct ported vacuum port or to none at all and just live with the residual mechanical advance built in to the dizzy (not recommended..but far better than making the mistake of running with it plugged in to manifold vacuum)

Ratch
05/06/10, 09:37 AM
To answer your questions, I use my vacuum gauge to set the timing for the highest possible vacuum (20 hg with the gauge hooked up to the hose running from the carb to the vacuum advance). However, when I check this with my timing gun, it looks to be set at 25 degrees (distributor nipple is pointing towards the passenger front headlight)...which seems really high.

The vacuume advance is plugged into the passenger side (towards the bottom) of the carburator and I do get constant vacuum at idle. If this is the wrong spot for it to be hooked up (this is how the PO had it set up), where should it come from?

I'll test the vacuum advance later tonight.

Dave

If you have 25* base timing at idle, you are way too advanced. Disconnect the vac advance and plug the hose, set timing to 10-12* with your timing light, then reconnect vac advance. that should give you an idea.

broncnaz
05/06/10, 10:35 AM
Ok just looked at 3 2100 carbs and 1 2150, none of the 2100's had a front vacuum port all were on the pass side and all are for ported vacuum. The 2150 had a port out the front. So you are hooked to the correct port as really you have no choice. I have a feeling that your throttle plate is open to far and is uncovering the port at idle which is why you see constant vacuum. You idle is probably set that high due to the timing being to far advanced and it wont run otherwise so Try this unhook the vac advance, plug the line and reset your timing and idle speed then recheck your timing. then make any needed adjustments to idle speed and fuel mixture. Now check your vacuum line does it still have full vacuum? If not hook the line back up if it does your idle speed is problably still to high.

Dave_in_Texas
05/06/10, 07:06 PM
Will do more work tonight, but did want to report the testing on the vacuum advance. I can move the distributor plate about 3/8 of an inch, cover the inlet, and it will pull back about half that distance (3/16 of an inch), stop, then when I move my finger, it pulls back into the original position.

So, I am getting some suction, so the diaphragm is still good, right?

Now its off to the store to do some mother's day shopping then back to the garage to reset timing like ya'll suggested!

Dave

vintage bronco
05/06/10, 07:20 PM
dave,
did you get my response in your other thread on the carb jets being tight ? how are you making out on it ?

Dave_in_Texas
05/06/10, 08:28 PM
Yes, carb jets are tight, very tight...probably too tight I can't get them out! But I don't need them out at this point. I'm headed to the garage to try some other things.

Dave

Dave_in_Texas
05/06/10, 09:42 PM
Partial success tonight!

I followed BroncoAZ's advice and:
1. Unhooked the vac advance
2. Plugged the line
3. Reset your timing
4. Reset carb to 1 1/2 out
5. Reset idle speed
6. Recheck your timing and make adjustment to mixture screws.
7. Final settings: 11-12* and the mixture needles 2 turns out each.

When all is said and done, I STILL had decent vacuum out the ported valve...about 15hg. When setting the timing, this was measured when the RPMs were really low with no throttle.

I also still would like to know now much suction I should have on the vacuum diaphragm. I tested it and the plate moved back half the distance, stopped, then went back to the original position when I let my finger off the inlet.

I took it for a test drive and it drove much better! I still need to keep the RPMs up a little more than normal when starting out, but no hesitation upon accelerating while at a cruising speed. I ALSO still have some popping in the exhaust at idle only.

Man, it was FUN to drive around again!! I missed that good 'ole Bronco smell...but my wife didn't. :)

Any other thoughts on:
-Decent vacuum from ported valve STILL. Why?
-Diaphragm...is it good or should the plate not move at all when testing it?
-Popping in exhaust at idle.

Thanks guys,

Dave

broncnaz
05/06/10, 10:17 PM
Sounds like the diaphram is good. As for the vacuum still present at idle speed well it could be that the throttle plates are still open to much even with a low idle if they cant be lowered anymore then the throttle plate may be bent or even out of alignment for some reason and is letting enough air by for the port to pick up a signal. I'd consider trying to find another carb to see if it makes any differance.
As for the popping in the exhaust at idle it could just be the idle mixture setting. the best way to set idle mixture is to turn each screw until you get the highest steady vacuum reading. Doesnt matter how many turns in or out the screws are 1 1/2- 2 turns out is just a base line setting that will usually allow the engine to idle.

DirtDonk
05/07/10, 12:30 AM
Doesnt matter how many turns in or out the screws are 1 1/2- 2 turns out is just a base line setting that will usually allow the engine to idle.

What he said. And remember too, that they do not have to be the same number of turns. You tune each one individually after the initial setting because, being a man-made mechanical device, there are differences and things change over the years anyway.
Because, as always, your results may vary.

Paul

DirtDonk
05/07/10, 12:31 AM
Oh, and perhaps the mechanical portion of your vacuum advance is worn out and loose? That could explain at least some of why your rod and plate move back part of the way.
Likely not the only thing at work here, but it's one possibility at least.

Paul

broncnaz
05/07/10, 07:52 AM
The breaker plate will have more travel than the vacuum advance does. Although a actual vacuum will pull it farther than my method of testing will as there will be some air left in the diaphram housing and you cant make up for that my test was only to test to see if the diaphram is in good shape or not. Most vacuum advances give around 10-12 degrees advance at the dizzy which is 20-24 degrees at the crank.

22213evl
05/07/10, 08:50 AM
try this

http://classicbroncos.com/forums/showthread.php?t=158487&highlight=carb

Dave_in_Texas
05/08/10, 11:05 PM
One other tid bit of info I forgot to mention. While I do still have vacuum at idle, when I rev the engine, the vacuum drops drastically and goes to zero.

Does info make sense to ya'll?

Dave

DirtDonk
05/09/10, 01:11 PM
Yes, that's what vacuum does. And exactly why most setups hate to run on full manifold vacuum.
As you open the throttle, vacuum signals naturally drop. Sometimes precipitously. The faster and farther you open, the lower it drops, until things equalize and your engine can pull more vacuum again.
Under very little load, such as level ground or just siting there, your vacuum will be relatively high. Under more load, such as going up a hill or towing a heavy load, the throttle blades are open farther and vacuum is lower.

The same theory holds true for ported vacuum of course, but it's modified by the port's location in the throttle bores. At low idle, there is zero vacuum. This is where you set the base timing. Just as you crack the throttle, instead of losing signal from it's max, you actually gain signal from zero to whatever. Not going to be full vacuum usually, but the initial spike is still fairly high and helps you accelerate and avoid bogging.
You still lose some signal as you push harder on the throttle, but that's perfect, as you want the ignition timing to fall back a bit from it's max vacuum-assist point, to avoid pinging.

Best thing for you would be to figure out why that port has full vacuum signal, or find another port that bleeds in from higher up in the throttle bore.
If you're able to remove the carb, you can trace where each port gets it's signal. Anything below the blades is full manifold vacuum all the time. Anything above them at idle is "ported".
Short of removing the carb, at least peer down the bores with a flashlight and look into each bore to see if you can see a slot (it's a transition slot you're looking for, rather than a single hole) and find out where it is in relation to the blades.
And verify too, that, with the choke all the way open, and the idle speed screw unscrewed to the point it's not touching the throttle lever, your throttle blades are closing literally all the way down so that there is zero gap on either side of the blade and the bore.
Something could be hanging them up and you're basing your idle on a falsely high setting.

Paul