Fuel System: Unusual Stromberg vacuum sound at low rpm

[tootie]

Good evening , I am curious about this sound and I just have to ask , even though I will be swapping out this Stromberg for another in the next week .My 60 Lark 259 , 2BBL , I have run and driven it in the last three months almost every day and have racked up 2000 miles . Car idles smooth , throttle plates are not worn out , pump shot is good and the engine runs great cold or hot . Gets about 18 mpg driving around town . Have owned and serviced countless cars with carbs and I enjoy making them run . My question to you Stude folks is simple . When I run the car at low speed with the oil bath air cleaner removed I hear the strangest vacuum sucking hissing sound which seems to be coming from the Stromberg WW. Today I put a tach on the car and set the idle at 900 rpm to test for vacuum leaks around the intake manifold and the base of the WW. I came up with no vacuum leaks anywhere .Is it normal noise ??? from the throttle plate in the WW??? To me the sound in not normal but I have never owned a WW before . Anyone a WW lover who cam give me some imput on this ??? Thanks , Joe in Tampa .

[StudeRich]

If there are no leaks from your "Exterior Testing", there is an Internal leak from a incorrect or blown Gasket or "other" internal issue.
Are BOTH Idle Richness Screws evenly adjusted?
I have found if if Runs with No change in speed with one closed, there are internal fuel passages that are clogged, not that yours is.

The only time I have heard one have a loud sucking sound was with Wide Open throttle under load with no Air Cleaner, sounds like a '50's or '60's V8 4 Brl. Police Car with an un-silenced Air Cleaner.

[tootie]

Well you are correct !!! I was a sheriff's mechanic for three years back when we had real police cars . WOT 440 Monaco with the top of the factory air cleaner flipped over was the sound of a speeding ticket on the way ! I have rebuilt probably 10 different popular carb models , including the Thermoquad and loving doing so . Sniper fuel injection failures are common in Florida , so I am not a fan of Holley . Facts are that idle mixture screws are both at 2 turns out and I set it with a tach and vacuum gauge . Runs vey well all the time and will idle down to 400 with no problem . This is just a really strange sound coming out of what appears to be the throat of the WW . I will bet money you are correct about a possible bad gasket somewhere . If I ever figure this out for certain I will let you know . Am builing a "new " WW this week and swapping it out . We will see !! NGU .....

[altair]

Rich is closest to the point, no vacuum leak is only part of the equation, a quick early test is to listen to the exhaust, ideally a smooth steady purr, any popping would indicate a vacuum leak. The excessive sound may be from a restricted internal tube or improperly assembled carb. I had a motorcycle carb apart three times, soaked it and blew it but still there was issues, but there were no vacuum leaks. With a close examination of some internal parts there was an obstruction in one of the small jets. Some time you have to think a little outside the box

[tootie]

Thanks for the input , as I say I am building a "new" carb this week and going thru it with a fine tooth comb first . I have never heard anything like this from any carb or intake . Will let yall know when I find it !

[tootie]

Base gasket was creating this noise , and I have never seen or heard this before . All I did yesterday was change out the really thick base gasket to a regular gasket and the noise stopped . Gasket does look kinda swelled up since I took it out . Never give up , and you will find the problem .