new to me car, quite a few questions (vacuum, carb, etc)

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Jan 21, 2020
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My Car
71 Mach 1 2V
Hi everyone,

The subject here is a new to me 1971 Mach 1 with a 2v 351C, factory ram air, AC (that has been converted to Sanden compressor) and allegedly 2bbl carb. 

This car is actually my dad's and I am trying to help him get some things sorted, but am a bit stumped in a few areas. 

Disclaimer/don't hate haha....I'm actually more of a BMW guy and haven't even seen a carb in about 18 years so please forgive my ignorance if a lot of this seems basic. 

I'll try to be terse. I did try to look a lot of this stuff up but this car doesn't seem to follow anything. Seems like the previous owner just kind of loosely cobbled whatever they felt like together and now I'm paying the price in terms of frustration.

1: the valve covers. Each of my valve covers has one of those "twist on" type holes that uses the gasket with the staggered tabs. What is supposed to go in each side? What it seems like I see most commonly is: 

passenger side: staggered type gasket with a push in breather

driver side: not sure on gasket (is there even one?) then oil filler type cap with integrated PCV to carb.

I have seen variations of the above so not sure if this is correct

2: fuel pressure regulator. Should I have this strange in line adjustable FPR? I don't see that on any pics and it seems like the original was all integrated into the carb. Is there any way to know how to adjust this since its in line? Not sure where I would tap in as I am used to newer stuff where you measure off a fuel rail. Car seems to be running rich but I think its because the vacuum system is not all plumbed correctly

3: Ram air air cleaner apparatus. The actual round metal part that the air filter sits in has 2 empty holes in the back passenger side. Is there supposed to be anything here on a 71? I have spent quite some time searching and can't find anything. I do have the vacuum pot in the snorkel that is connected to a 4-way metal tee coming out of the back of the manifold.

Also, there is a screw in the snorkel that prevents the flap from being more than about 75% closed. Should I put in a shorter screw? Take it out? 

I see on a lot of diagrams a mention of a "bi metal sensor" that to me looks like its in or attached to the air cleaner. 1) I don't seem to have one of these as far as I can tell and 2) I can't find the part number or anything in order to get one. Is this what goes in one of the 2 blank holes?

4: carb. This appears to not be an original carb at all. Any idea what it is? Don't see a manufacturer name anywhere.

5: vaccum diagram. I have looked at every vacuum diagram I can find, including the PDFs available on this site. I can't seem to find one that matches exactly what I have. I have a 4 way vacuum tee in the back of the manifold connected to: brake booster (larger tube), ram air vacuum pots (Y'd), some hard line going behind the engine (trans?), and the air cleaner snorkel vacuum pot. 

There is a single vacuum port on the front of the manifold that is capped. 

The distributor appears to *not* be one of the vacuum advance/retard units that has several vacuum lines. There is only a single port coming off the silver diaphragm on the front, that goes directly to one of the ports on the front of the carb. 


Front of carb: There are 2 small ports and 1 larger port in between them. Driver's side small goes to distributor silver diaphragm. Middle larger port goes to PCV which is inserted into the top of some sort of stainless steel breather (some white fibers inside), screwed in kind of loosely with no gasket in the front of the driver's side valve cover.  The passenger side small port is capped off. 

Passenger side of carb: 

Large vacuum port on the middle top is connected to nothing and is not capped. The smaller vacuum hose that is nearer the firewall....Can't remember what this goes to at the moment. And then next to that is the fuel in line

Back of carb:

No ports, just one large screw with a flat head groove in it screwed in the middle bottom


Single vacuum port in the front, on pass side of distributor: this is capped

4-way tee near firewall: Large hose to brake booster. Driver's side small hose to ram air vacuum pots in hood. Middle small hose to hard line going under firewall (trans?). Pass side small hose to vacuum pot in air cleaner snorkel. 

Here are some pics of the above. I know this post is long so I apologize for that. If anyone can help clear up any of this I would be most appreciative! 

Thanks in advance







Jan 1, 2012
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Eugene, OR
My Car
1971 Mustang Sportroof M code
I'll start it off by saying that the carburetor looks like an old Carter AFB 4-barrel carburetor, so someone in the past switched it from a 2-barrel to a 4-barrel carburetor.

For the most part the vacuum looks correct, except there should be a connection to a 2 or 4 port vacuum manifold on the firewall, that the AC and transmission vacuum modulator connect to.

I don't have time to go into details on each one of your questions, so hopefully someone else will.

One other thing, the PCV connection from the twist-on cap on the driver side manifold to the carburetor is correct, the twist on cap on the other side should have a hose that connects it to the air cleaner for a fresh air supply to the crankcase.

Welcome to the forum, please go to the introduction section and introduce yourself and your car, we like pictures.

Jan 7, 2015
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Western North Carolina
My Car
Multiple Mustangs!
Wow you have lots of questions. I see your location is South and you say you are a BMW guy. By chance are you located in S.C. near the BMW assembly plant? I am in Hendersonville, NC and have several cars. If you are close might be easier to come visit and look at what you need to review. 

The fuel pressure regulator is something someone added and should not be needed unless they installed an electric pump in the tank or somewhere else. The stock fuel pump was originally a Carter and no regulator. 

Also most on here advise you to eliminate the plastic gas filters. Some crack due to the ethanol in the fuel and that is bad to have gas all over a hot running engine. 

I lost a bunch of pics due to computer crash but I have three assembled mustangs here to view and lots of parts.

Apr 24, 2013
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My Car
1971 J Code Mach 1
1972 H Code Mach 1
Oh boy you are in for some detective work!

My $0.02 is to split your repairs into systems and go from there:

1) PCV system- I am not 1000% sure, but I think on a 351C you should have one VC with jusyt a push-in gommet with a plastic elbow that should have a section of rubber hose that connects to a nipple on the air filter housing that is part of a filter (not the air filter). As Don mentioned, this is where the crankcase is fed fresh filtered air to replace that ingested by the engine through the PCV valve. Let me try and find some pics:

2) Fuel system- as mentioned, if your car is in fact an 'H' code, somebody has swapped the intake to one for a 4V carb. I think you should figure out what kind of fuel pump is on the engine as some high output pumps need a regulator to reduce the pressure so that the pump doesn't lift the needle off of its seat and flood the engine. Also, maybe someone can chime in on what carb you have (I just know it isn't a Holley!:) ) so that you can figure out if your fuel pressure is ok...

3) Vacuum system- If your car was built with AC it should have a small canister under the passenger side hood hinge that is fed from the manifold referenced above. The HVAC box dashpots run off of this canister so if you still have the facotry AC stuff and it works its getting vacuum from somewhere else.

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