1970 302 Manual - Low Idle & Vacuum Lines

[tonytony9]

Hi Everyone,

First off, I want to preempt too advanced feedback (lol) by stating I am an amateur eager to learn.

Current Setup: 1970 302, Manual Transmission, Autolite 2100 2b Carb, no a/c

Recently redid the intake manifold gasket due to leaks out front passenger side corner and rear. Prior to intake manifold job, the truck idled too high. Would take forever on a semi cold day (mid 35 F) to step down. Sometimes "accelerating itself" even after warming up.

Post intake manifold job by mechanic, truck is stalling under a few circumstances: when approaching a stop light, shifting from third to neutral it seems to slowly stall upon approach as idle drops. When switching from 3rd to 2nd gear around the lower rpm band of third gear to drop it into 2nd. From neutral into reverse or slipping into 1st, need to rev up a bit.

The mechanic noted that the double port vacuum advance needs to be replaced. I am wondering if PO had idle set high because of what appears to be a mess of vaccum lines.

The Goal: Straighten out all vacuum lines and correct normal idle.

1. I have been trying to find a detail vacuum diagram. I found a manual for the 2100 if anyone is interest: Autolite 2100 Manual
2. What is the best way to diagnose and tackle this?
3. Do you know which vacuum advance for the distributer I need to buy?

Media Link: https://drive.google.com/drive/folders/1DPiCXVG1rf8DJeLH3_NdG-T82_UZKeux?usp=sharing

 

[DirtDonk]

Well first, on a 70 bronco there really aren’t many vacuum lines.
The fact that it has the dual advance/retard setup on the distributor though, means that it would have more than normal. Three or four at the most theoretically.
You wouldn’t even have had a vacuum brake booster, or automatic transmission modulator to deal with. Only a PCV valve and vacuum advance lines that I can recall.
Can you show a picture of yours? Is it set up as original as far as you can tell?
There would’ve been a vacuum diaphragm spring loaded thingy with a blue cone shaped cover on it, bolted to the back of the intake manifold with, if I remember, three vacuum lines.
There would also be a small vacuum manifold (later a vacuum “tree“) threaded into the back of the intake manifold.
It’s a finicky little setup, so you could try bypassing it at least temporarily, by simply running the front vacuum port on your advance mechanism canister, to the ported vacuum fitting on the carburetor.
I forget which one exactly that is on a 2100, but someone here will know.
Especially if you show us pictures.

Thanks

 

[DirtDonk]

Oops! Sorry, I didn’t look at your media link first. Thanks for the pics!

 

[DirtDonk]

OK, I see a couple of things I would address right away.
One is, as I mentioned earlier, you might as well just use the advance mechanism instead of the advance and retard mechanisms.
Your little blue thingy is not fully connected anyway, so is not functioning properly. You need to plug all the hoses and ports from the little brass vacuum manifold. Then either disconnect the hose from the rear, most port on the vacuum. Advance can or simply leave it in place, but disconnect it from any vacuum source or other equipment.
Then find the ported vacuum fitting on the carburetor, and connect it to the advance fitting, which is the front most hose fitting on the advanced canister.

Before you reconnect the vacuum, set the idle up and check your timing. They may have said it at the stock setting, which may mean you can benefit from a little more advance.
Since you had someone else do the work, are you able to check timing and idle speed? If you don’t have the tools, but you know how to do it, maybe you can get one of the loaner timing lights from one of the auto parts chains.

The problem is you’re describing with idle, could be that the idle speed is too low to begin with. It also could mean that your spark is a little weak.
Things are looking pretty old on that engine, so you may have to do some other things as well.
Checking the timing for accuracy is one good place to start. But also, those plug wires look pretty ancient. Maybe check them with an ohm-meter.
Or when in doubt, just replace them.
The problem with that of course is, that you could get a bad one. But, good new ones would be beneficial.
I believe you said you are still running points ignition in the distributor? Or is it converted to electronic? If not, now might be a good time to switch over.
Unless you like fiddling with things.

Another thing I noticed with the pics, is that the downward angled hose fitting on the back of the carburetor doesn’t have anything going to it.
That is for clean air to go into the exhaust manifold to get heated to then go back to the choke housing. Not having that connected could be one of the reasons it takes so long for the choke to heat up when it’s cold outside. That, along with the heat riser hose from the exhaust manifold that I can see near the front, that is supposed to run up to the snorkel on the air filter housing.
Do you have one of those?
If you do not have a hose running down to the exhaust manifold to the fitting on the back of the carburetor, cap that fitting off because it is simply allowing dirty air into the carburetor every time the engine is running.
Very important!

And last, can you get a better picture of the passenger side valve cover? I just wanted to see if you have a PCV valve connected.
I see a PCV valve hose on the carburetor, but just curious about the valve itself.

Thanks.

 

[B RON CO]

Hi, I would think that the ignition timing is off, since the distributor was removed to replace the intake manifold gasket. So, as mentioned, I would hook the vacuum hose from the front nipple on the distributor canister to the vacuum nipple on the right side of the carb, in front of the choke (ported vacuum), and eliminate the inner hose (vacuum retard). When you get your hands on a timing light, set the base timing to @ 12* advance, with the vacuum hose removed from the distributor and plugged. Check the vacuum advance canister with a hand vacuum pump, or just suck on the hose. With the distributor cap off, you should see the breaker plate move. If there is no movement the vacuum canister should be replaced. With the engine running the timing marks should move up when you give it gas. You can see this with the timing light.
The ignition must be in top tune before getting to the carb, so if you have no idea when the last tune up was, I would get top quality cap, rotor, plugs, wires, and possibly a Pertronics II ignition.
Why is the choke closed in the pictures. If the engine was cold, OK, but when the engine is warmed up the choke should be wide open and held open by spring pressure. When the choke is fully open the high idle cam should be disengaged. Then you can adjust the idle speed, mixture screws, and that dashpot. If the choke and high idle is sticky, you can spray it with some WD 40.
Good luck

 

[tonytony9]

OK, I see a couple of things I would address right away.
One is, as I mentioned earlier, you might as well just use the advance mechanism instead of the advance and retard mechanisms.
Your little blue thingy is not fully connected anyway, so is not functioning properly. You need to plug all the hoses and ports from the little brass vacuum manifold. Then either disconnect the hose from the rear, most port on the vacuum. Advance can or simply leave it in place, but disconnect it from any vacuum source or other equipment.
Then find the ported vacuum fitting on the carburetor, and connect it to the advance fitting, which is the front most hose fitting on the advanced canister.

Before you reconnect the vacuum, set the idle up and check your timing. They may have said it at the stock setting, which may mean you can benefit from a little more advance.
Since you had someone else do the work, are you able to check timing and idle speed? If you don’t have the tools, but you know how to do it, maybe you can get one of the loaner timing lights from one of the auto parts chains.

The problem is you’re describing with idle, could be that the idle speed is too low to begin with. It also could mean that your spark is a little weak.
Things are looking pretty old on that engine, so you may have to do some other things as well.
Checking the timing for accuracy is one good place to start. But also, those plug wires look pretty ancient. Maybe check them with an ohm-meter.
Or when in doubt, just replace them.
The problem with that of course is, that you could get a bad one. But, good new ones would be beneficial.
I believe you said you are still running points ignition in the distributor? Or is it converted to electronic? If not, now might be a good time to switch over.
Unless you like fiddling with things.

Another thing I noticed with the pics, is that the downward angled hose fitting on the back of the carburetor doesn’t have anything going to it.
That is for clean air to go into the exhaust manifold to get heated to then go back to the choke housing. Not having that connected could be one of the reasons it takes so long for the choke to heat up when it’s cold outside. That, along with the heat riser hose from the exhaust manifold that I can see near the front, that is supposed to run up to the snorkel on the air filter housing.
Do you have one of those?
If you do not have a hose running down to the exhaust manifold to the fitting on the back of the carburetor, cap that fitting off because it is simply allowing dirty air into the carburetor every time the engine is running.
Very important!

And last, can you get a better picture of the passenger side valve cover? I just wanted to see if you have a PCV valve connected.
I see a PCV valve hose on the carburetor, but just curious about the valve itself.

Thanks.

Hi, I would think that the ignition timing is off, since the distributor was removed to replace the intake manifold gasket. So, as mentioned, I would hook the vacuum hose from the front nipple on the distributor canister to the vacuum nipple on the right side of the carb, in front of the choke (ported vacuum), and eliminate the inner hose (vacuum retard). When you get your hands on a timing light, set the base timing to @ 12* advance, with the vacuum hose removed from the distributor and plugged. Check the vacuum advance canister with a hand vacuum pump, or just suck on the hose. With the distributor cap off, you should see the breaker plate move. If there is no movement the vacuum canister should be replaced. With the engine running the timing marks should move up when you give it gas. You can see this with the timing light.
The ignition must be in top tune before getting to the carb, so if you have no idea when the last tune up was, I would get top quality cap, rotor, plugs, wires, and possibly a Pertronics II ignition.
Why is the choke closed in the pictures. If the engine was cold, OK, but when the engine is warmed up the choke should be wide open and held open by spring pressure. When the choke is fully open the high idle cam should be disengaged. Then you can adjust the idle speed, mixture screws, and that dashpot. If the choke and high idle is sticky, you can spray it with some WD 40.
Good luck

Thanks for the input. It has taken me sometime to get back around to this project. I am doing this along with a suspension/steering overhaul. I want to confirm a few things to make sure I am understanding this correctly. Distributer and points looker newer. Plug wires also newer as well as spark plugs. If fixing the vacuum equipment does not solve the issue that will be my next move along with renting a timing gun.

Currently, I have the front most port on the vacuum advance plugged into the left side of the carburetor. I believe you mention this is the ported vacuum fitting. I also noticed there is another port on the left side of the carburetor, it appears to be plugged. See below pictures.

Next, I have the rear port on the vacuum advance not connected to anything. Should I leave this unplugged and not connected to anything?

Next, I believe you are recommending that I bypass the blue cone thing and the Tree on the back of the intake manifold. Right now, I have both ports on the Tree plugged. The blue cone is completely bypassed, not doing anything from what I can see.
See below pictures.

Lastly, I believe you are suggested that I connect the front part of the passenger side exhaust manifold to the below port on the air cleaner. Is this correct?

Do I have the setup correct?


One more thing, I tried blowing air through the tubes on the vacuum advance and did not find any movement within the distributer. So, I am planning on replacing it. Where can I buy a dual port vacuum advance? I am having trouble locating one.

 

[Oldtimer]

One more thing, I tried blowing air through the tubes on the vacuum advance and did not find any movement within the distributer. So, I am planning on replacing it. Where can I buy a dual port vacuum advance? I am having trouble locating one.

You need to apply vacuum to the hoses on distributor to see movment.

https://www.amazon.com/dp/B07D2B13DF/?tag=classicbroncos-20

 

[tonytony9]

You need to apply vacuum to the hoses on distributor to see movment.

View attachment 925384

https://www.amazon.com/dp/B07D2B13DF/?tag=classicbroncos-20[/URL

http://Ah I thought the blow trick would apply enough pressure to get a little play. Thanks.

 

[tonytony9]

Can anyone confirm if my pictures above represent the correct setup?

 

[Oldtimer]

 

[DirtDonk]

Sorry Tony. Meant to address some of those pictures the other day, but I never made it back to my computer. It’s just easier for me to work on the computer than my phone, but I’ll see what I can do in the meantime.

Oldtimer’s diagram shows the correct, original way to connect all those devices. But for the time being, to make sure we rule out any other faults, I wouldn’t bother to try to reconnect at all the factory away. Not just yet anyway.
I would keep everything plugged off and set your timing and carburetor settings, first without the vacuum advance connected.
Then recheck everything after it’s connected the simple way.
Then later, if you so desire, you can reconnect it all as it was originally.
Wouldn’t hurt to have new hoses at that point either, unless the ones you have look to be in good shape. They look pretty decent from here, but only you’ll be able to tell their condition directly

 

[B RON CO]

Hi, the large tube from the exhaust to the air filter housing is to aid warm up in cold weather. Many guys do not have it. I would remove the vacuum hose from the tree on the back of the intake manifold to the blue cone and plug it, There may be a vacuum leak in the old emission system. If you do not have a vacuum hand pump you can suck on the hose going to the front nipple on the vacuum advance canister to test it, Good luck