mechanic question

[tatonka]

I have a 1976 Ford F250 with a 390 and a holley carb 4 barrel ,that it came with stock . When taking the air cleaner off you can hear a loud vacuem leak . I cover the barrels till it almost chokes out ,and the sound dies down alot . I just returned from Oregon country fair , and decided to check it over before BM . The trip to OCF was 100 miles , it ran well , got 14 miles to a gal. and was hauling my camper, also the temp is good and idles ok . Pulled a plug out, and it looked great .
Dont want to mess with it to much cause its getting 14 mpg , ( straight road , no hills ) I have a brand new 2 barrel with adaptor . So I will bring it along just in case

[Token]

Are you sure that isn’t just the normal breathing of the barrel through the closed butterfly?

They do make a wee sucking sound in normal operation.

[motskyroonmatick]

It's been a long time since I looked down the barrels of a 390 but I distinctly remember I could hear the sucking sound.

[XPTom]

https://www.2carpros.com/articles/how-t ... cuum-gauge



or google carb spray + vacuum leak and pick one of many similar posts. Wear eye protection and spray while exhaling so you don't inhale a kaboom....

[tatonka]

its kinda high pitched for a normal sound , very noticeable with air cleaner off . My other old fords never made that sound , but none of them had a holley carb.

[Jackass]

If it's running that good and the idle speed is right where it should be, it's probably just the sound of the air passing through the carb. Check the vacuum brake booster hose and pcv line carefully, those can crack where you don't see it... other than that spray a little carb clean around the base of the carb to check for leaks. Not too much carb cleaner and try to keep it away from those plug wires and exhaust manifolds, (use the little red straw) you don't want a flash fire.

[Token]

its kinda high pitched for a normal sound , very noticeable with air cleaner off . My other old fords never made that sound , but none of them had a holley carb.

The fact you gotta take the air filter to hear it better indicates the sound is originating in the bore of the barrel.

I’d say your likely good.

Now, checking the vacuum lines is always a good thing.

[tatonka]

its kinda high pitched for a normal sound , very noticeable with air cleaner off . My other old fords never made that sound , but none of them had a holley carb.

The fact you gotta take the air filter to hear it better indicates the sound is originating in the bore of the barrel.

I’d say your likely good.

Now, checking the vacuum lines is always a good thing.

thanks , replaced one line already , have to get a gasket , then start it and check with the carb spray , thks all

[Token]

Make sure you follow these S3 rules, as this is all Playa related.

1. Whiskey and/or Whisky are required. 1cc every 5 minutes for the first hour will meet the minimal acceptable standards of S3.

2. PBR ice cold to maintain hydration.

3. Have a friend come over and hold the 20# ABC extinguisher in one hand and his PBR in the other. Yell and curse profusely when said friend pulls the pin from the extinguisher in order to save 300 milliseconds of response time. “That is fucking expensive”!

4. Wear next to no clothing while doing this. Naked, if at all possible, is in line with S3 doctrine.

5. Have second friend film everything.

6. Have third friend show up in the middle of the testing and proclaim: “Dude, if I light a fart and you catch it with the carb cleaner spray” ...

... who trucking needs the Playa anyway?

All the glorious S3 points were added to make item 3 in bold more interesting. Seriously though, fire extinguisher within reach at all times.

[Elliot]

It's been a long time since I looked down the barrels of a 390 but I distinctly remember I could hear the sucking sound.

And you are not talking about intake manifold vacuum, are you?

It has been a long time since I lifted the intake manifold off a 390, but I can still feel the hernia.

[tatonka]

had some beers , then replaced some vac lines . Fired it up and no noise..............untill it warms up then its a good shrill whistle coming from inside the 2 barrel side of carb . Oh well it runs ok and the noise is hardley there with the air cleaner on , so I will chance it , plus I have the extra carb I have a edelbrock manifold for the 390 , glad its alum

[Jackass]

Oh yeah, it's usually a good idea to snug up the carb bolts/ base nuts, or make sure they're snug too

[mgb327]

Turn up the radio and just go for it.

[Captain Goddammit]

i also agree that if you can only hear it with the air cleaner off, it’s not likely an external vacuum leak.

You can use WD40 to spray and check for vacuum leaks without much hazard of unplanned fires.

14 MPG is pretty stellar for an old F250 with a 390.

[ygmir]

does it change if/when you operate the throttle?
If so, it's probably "ported vacuum", above the butterflies, and won't be a big issue.
Also check in the venturies for any small item that might disrupt the flow, or cause a whistle....
I'd agree with the others, according all your checks and info, it's running fine.
Also, try pinching off the "ported vacuum" line(s) off the carb to see if it stops. As I recall, there should only be one, and it'd go to the distributor, for vacuum advance. Note the port for it will or should, be higher on the carb than the butterfly.
Good luck!

[tatonka]

Thanks all

[Burnrider]

use a spray water bottle on all vacuum lines and around carb base with filter on if a change in the intake sound or engine falters its external lines or gasket leaking your vacuum unbalancing the air ratio do it again with filter off and see the difference sound or no change and track it down some vacuum lines are not near your carb i.e. smog shit or other device it must b fixed or ok by now