Vacuum Leak

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Clunker
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Vacuum Leak

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I have suspected since day 1 that I had a vacuum leak in my F250, and today I finally had a chance to track it down. My timing light is broken, so I can't see if the distributor is advancing, but I couldn't detect any vacuum in the line leading to the vacuum advance diaphragm, and I discovered what I think is a gaping hole (hence the lack of vacuum). Can you guys look at this picture and tell me if this is a vacuum connection that needs to be capped? It's been a while since I've worked on carburetors, and the last ones were side drafts. I circled the spot in bright green. Thanks

Image
1970 F250 CS: 360, RV cam, Edelbrock Performer 390 intake, Holley 600, headers, Pertronix II, Flamethrower coil.
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sargentrs
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Re: Vacuum Leak

Post by sargentrs »

There should not be an open port on a carburetor anywhere. Cap it or connect it. Is that on a spacer under the carb or on the carb itself?
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1970 F100 Sport Custom Limited LWB, 302cid, 3 on the tree. NO A/C, NO P/S, NO P/B. Currently in 1000 pcs while rebuilding. Project thread: http://www.fordification.com/forum/view ... 22&t=59995 Plan: 351w, C4, LSD, pwr front disc, p/s, a/c, bucket seats, new interior and paint.
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Re: Vacuum Leak

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Thanks for the response. That was my thinking as well, but I wanted to make sure. The port is coming out of a 1" spacer below the carburetor. I wonder how much junk has been sucked into the engine over the years.
1970 F250 CS: 360, RV cam, Edelbrock Performer 390 intake, Holley 600, headers, Pertronix II, Flamethrower coil.
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Re: Vacuum Leak

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If that's original to the truck, and it's an FE engine, that spacer is probably part of carb heater setup. Here's a thread from another member that kind of explains it. http://www.fordification.com/forum/view ... p?p=522602
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1970 F100 Sport Custom Limited LWB, 302cid, 3 on the tree. NO A/C, NO P/S, NO P/B. Currently in 1000 pcs while rebuilding. Project thread: http://www.fordification.com/forum/view ... 22&t=59995 Plan: 351w, C4, LSD, pwr front disc, p/s, a/c, bucket seats, new interior and paint.
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Re: Vacuum Leak

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Thanks for the link. It sounds like that port is probably for the spacer heater mentioned in the other thread. Capping it made no difference. However, disconnecting the vacuum line from the carburetor to the vacuum advance also made no difference. It runs the same and has the same lack of power. I'm guessing that my vacuum advance is not functioning at all. The diaphragm looks old and rusty, so it wouldn't surprise me if it's no longer functioning. The advancing mechanism within the distributor looks good and appears to work fine, but the spring feels awfully strong for a vacuum to overcome. I'm new to the Ford engines, so any suggestions are always appreciated.
1970 F250 CS: 360, RV cam, Edelbrock Performer 390 intake, Holley 600, headers, Pertronix II, Flamethrower coil.
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Re: Vacuum Leak

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There's differring opinions on whether to run "ported" vacuum vs manifold vacuum to hook up to the vacuum advance. Personally, I run manifold vacuum. You might try pulling the line from Carb, capping the Carb port, and running the vacuum advance to manifold vacuum as a final check before going to the trouble and expense, although minimal, of rebuilding the carb or replacing the vacuum advance. Either that or get a hand held vacuum pump and test the advance.
Randy
1970 F100 Sport Custom Limited LWB, 302cid, 3 on the tree. NO A/C, NO P/S, NO P/B. Currently in 1000 pcs while rebuilding. Project thread: http://www.fordification.com/forum/view ... 22&t=59995 Plan: 351w, C4, LSD, pwr front disc, p/s, a/c, bucket seats, new interior and paint.
1987 F-150 XLT Lariat, 5.0/C6 auto.
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Re: Vacuum Leak

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I think I saw an available port (capped) coming off the manifold, so maybe I'll try that first. The power brakes and power steering both work fine, and their vacuum lines come off of that same manifold junction. Just having a functional timing light would be very helpful in diagnosing timing issues. I guess I could just run to the store and buy a new one, but my Dad bought this one back in the late 70's and gave it to me sometime in the 90's. When is the last time you saw a chrome-plated metal casting anything. As far as the diaphragm, they're pretty cheap and easy to replace, so I'll just pick up a new one and rule out one of the possible problems. Thanks for your help.
1970 F250 CS: 360, RV cam, Edelbrock Performer 390 intake, Holley 600, headers, Pertronix II, Flamethrower coil.
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Re: Vacuum Leak

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sargentrs wrote:Either that or get a hand held vacuum pump and test the advance.
This is exactly what I did. I already had a Mity-Vac, and a vacuum gauge, so I bought some vacuum tubing, and tee'd my distributor to the vacuum gauge and Mity-Vac. Found out I needed 7" of vacuum to completely advance the vacuum advance for my distributor.
Clunker wrote:The power brakes and power steering both work fine, and their vacuum lines come off of that same manifold junction..
The power steering doesn't use the vacuum, does it? I thought it got everything from the steering pump driven off of a fan belt. Or am I misunderstanding?

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"Sugar", my 1967 Ford F250 2WD Camper Special, 352FE, Ford iron "T" Intake with 1405 Edelbrock, Duraspark II Ignition, C6 transmission, front disc brake conversion.
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Re: Vacuum Leak

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You might be right about the power steering having nothing to do with vacuum. I saw two large lines coming from the manifold. One of them definitely goes to the brake booster, but I didn't really investigate where the other one went. I don't have any type of vacuum to test the diaphragm, and I think a new vacuum advance costs less than the vacuum to test it, so I'll just pick up a new one. Thanks for the help guys. I really appreciate it.
1970 F250 CS: 360, RV cam, Edelbrock Performer 390 intake, Holley 600, headers, Pertronix II, Flamethrower coil.
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Re: Vacuum Leak

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Clunker wrote:I saw two large lines coming from the manifold. One of them definitely goes to the brake booster, but I didn't really investigate where the other one went.
Just a guess without pics, but PCV valve for the other large line? Kind of weird to come off the manifold, though; the PCV usually goes up by the carb. But if you still have a large, uncappe line going to the intake manifold, you need to cap it, at the very least. Do you have pics of this second line?
Clunker wrote:I don't have any type of vacuum to test the diaphragm, and I think a new vacuum advance costs less than the vacuum to test it, so I'll just pick up a new one.


I know, but there are SO many uses for a Mity-Vac, and you need a vacuum gauge, even if you don't know it yet. It is the do-all tool for engine work. Tests for cylnder issues (valves, rings), ignition timing, restricted exhaust, vacuum leaks, carb adjustments, etc.

Keep us posted,

Joseph
"Sugar", my 1967 Ford F250 2WD Camper Special, 352FE, Ford iron "T" Intake with 1405 Edelbrock, Duraspark II Ignition, C6 transmission, front disc brake conversion.
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Re: Vacuum Leak

Post by BRUTUS_T_HOG »

Isn't the vacuum which you connect to the distributor dependent on design and application? Some require manifold vacuum or ported vacuum? I believe these use ported vacuum.
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Re: Vacuum Leak

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BRUTUS_T_HOG wrote:Isn't the vacuum which you connect to the distributor dependent on design and application? Some require manifold vacuum or ported vacuum? I believe these use ported vacuum.
I have found that the choice of which vacuum source to use is kind of like threads discussing which oil is best. Wars have been fought on such topics! Ported vacuum is for emission control, and these trucks are pre-emission! No, ported vacuum was developed back in the 30's before they worried about emissions! No, my engine idles smoother with manifold vacuum! No, it advances the spark too far at idle; you'll burn your valves up! No, you got chocolate in my peanut butter!

By the way, Shell Rotella was great in my Duramax, but it stank; I really liked Mobil 1, but it was hard to get; Chevron Delo was noisy; and Amsoil was too expensive! None of them affected performance, so the bottom line was to flip a coin ... And for the record, my distributor is connected to ported vacuum (for now), although I have experimented some with manifold vacuum.

Joseph
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Re: Vacuum Leak

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Every vacuum related port that I can find on the engine has either a line running to it or a cap. It might be the PCV valve line running to the manifold, but I thought it was supposed to run directly to the carburetor. I'll try to take another look soon (maybe get some pics), but it's a busy week.

Funny you should mention Amsoil being too expensive. I used to think the same thing, but conventional motor oil around here costs more than $5/qt., and I can get full synthetic through Amsoil's website on their frequent buyer program for about $7/qt. (better than I can find any other synthetic locally).

I still have to do a lot more investigation of the truck. Considering that the previous owner said that he never changed the oil, the radiator was short more than a gallon, only one of the five aftermarket gauges reads correctly, the transmission fluid barely registered on the dip stick, the rear view mirror was missing, the side mirrors collapsed toward the windows as soon as you hit 20 MPH, and flipping the gas tank switch blew a fuse; I have my work cut out for me.

It's true that the stock engine used a line from the carburetor for the vacuum advance. It's also true that many Ford owners on this forum advance their timing several degrees before the stock setting, or have installed electronic ignition, or have otherwise modified their engines to increase the efficiency. I think running a line from the manifold instead of the carb is worth trying.
1970 F250 CS: 360, RV cam, Edelbrock Performer 390 intake, Holley 600, headers, Pertronix II, Flamethrower coil.
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Re: Vacuum Leak

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***Update***

I finally had a chance to look at the vacuum lines this morning. There are two lines coming directly from the manifold; one to the brake booster and one to the transmission. As suspected, there is also a third port (the correct size for connecting to the vacuum advance) that was capped. I also found two very important problems. The cap was split, and the line running to the transmission was very loose, but I didn't see any splits in the line. A hose clamp should solve the problem. I removed the vacuum advance and found that it is probably still functional since it moves air. I'm going to fix the vacuum leaks and see if the distributor advances.

The port pictured at the beginning of this post is definitely a coolant line for the carburetor spacer. An identical port runs out the back of the spacer. I'm not sure when it was disconnected, but I may run a bypass line to it since we get cold weather here. Thanks to everyone for the help. I'll let you know what happens later today.
1970 F250 CS: 360, RV cam, Edelbrock Performer 390 intake, Holley 600, headers, Pertronix II, Flamethrower coil.
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Re: Vacuum Leak

Post by Clunker »

Problem solved. There is no longer a hesitation when I step on the gas, so I think the vacuum advance is working properly. I still have a lot of tweaking to do, but she's ready for fishing season. I left the vacuum line connected to the carburetor instead of the manifold, but I may tinker with it a bit to see if one setup performs better than the other.
1970 F250 CS: 360, RV cam, Edelbrock Performer 390 intake, Holley 600, headers, Pertronix II, Flamethrower coil.
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