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Discussion Starter #1
Hi guys, i've had this noise develop on my 70 FB, 351C that's got a little worse in the last few outings in the car.

I'm thinking vacuum leak but I didn't have time today to investigate fully but at a quick glance I didn't notice anything obvious, the car is running fine when driving but at idle is running a little rough and the RPM is fluctuating slightly on it's own.

The noise doesn't sound like it's internally in the block or anything, it definitely sounds like something on the outer areas, sounds like approximately at the back of the carb type of area near bulkhead.

Please see below videos, the noise actually sounds worse in the video but still noticeable in person.

If it is vacuum any tips on locating where abouts as i've never tackled vacuum leaks before.

Thanks for any help.


 

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Discussion Starter #2
So listening on the stethoscope it sounded like it was coming from the carb area, so i've changed the carb gasket but the noise is still there, any ideas ? Thanks
 

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1967 Mustang Convertible
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Sounds like a vacuum leak. Get a spray bottle and start spraying water around the lower intake and carb area and see if the noise changes and you find where its coming from. I like to use water since easy to clean up.
 
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Worn primary throttle shaft or base plate (if no bushings to support shaft).
 

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Sounds like a vacuum leak to me as well. I use carb cleaner, as it'll cause the idle to change when it gets sucked into the vacuum leak. Evaporates quickly with no residue.

As @Woodchuck recommended, check the throttle shafts. Spray a little carb cleaner on them where they exit the baseplate and see what happens.
 

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Have you checked the vacuum with a gauge?
Carb cleaner works well, but it is a fire hazard. Be very careful! An alternative is propone torche. Attache a fuel hose so you can reach all areas and open the bottle a bit. This is less risky compared to carb cleaner. Of course the water bottle is the safest option.
 
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