The Stovebolt Site Forums The Shop Area Engine Shop Whistling at part throttle

1962 235 engine. 1951 truck. Carburetor is a YF 2100s. I have the larger 3 piece oil bath with a modern paper element in it.

I get a very pronounced and a annoying whistle at almost any throttle positions except for idle and WOT. My hypothesis is that something about the air cleaner results in this noise. I need to take a test drive without the air cleaner and/or with the smaller “true” oil bath I have to test that hypothesis.

In the meantime, any guesses or pointers on where to start looking?

I’m fairly familiar with the normal sounds of a carbureted engine. This seems unique and abnormal to me.

As you suggested, drive it with the air cleaner completely removed and you'll have your answer.

If it still whistles, it's probably a vacuum leak somewhere (carb base to manifold, throttle body to base, etc).

Does it whistle when you rev the engine in the garage above idle?

I had a similar problem a few years back. The whistle turned out to be a small vacuum leak at the air horn gasket due to warpage.

Air horn to air cleaner?

Spray some carb cleaner all around the potential vacuum leak spots while the engine is running and see if the rpms change. If they do, you have a vacuum leak.

Did the spray thing a while back. No leaks detected.

I believe this to be an air leak above the throttle plate, or just a function of the way air is entering the air filter, and not necessarily a vac leak.

Well then, drive it without the air cleaner installed and you'll know instantly whether that's the cause or not.

Whistling is actually worse with the air cleaner removed. I will try the smaller oil bath I have, that is still an oil bath, see if that changes anything.

If it's whistling without the air cleaner, the air cleaner isn't the problem. Your carburetor has a vacuum leak.

You might be right. Maybe an air leak around throttle shaft that only presents at certain levels of opening.

Or it might be some oddity in how the air flows around the choke or throttle plate. Gonna take some more figuring and head scratching.

The reasons I’m not fully persuaded that it’s a “true” vacuum leak (of manifold vacuum): carb spray test doesn’t indicate one, vac gauge doesn’t indicate one, idle quality is unaffected, and it happens when manifold vac should be fairly low.

If you still have vacuum wipers check both ends of the hose.

My Packard developed the same whistle. Carb cleaner didn't show a leak either.

I took the carb off and snugged up all the screws holding it together (the center section attaches to the base with screws from the bottom so it can't be done on the car).

That cured it right up. The leak wasn't enough to make the car run rough, just enough to make an annoying whistle.

I told people it was the supercharger winding up.

Teach it to whistle your favorite tunes

Slightly loose carb bolts (as mentioned in above post) or a vacuum leak somewhere can cause the whistle.

History (or trivia which you probably did not wish to know):

In the early days of motoring, many cars whistled. Hudson had a carburetor manufactured for them by Detroit Lubricator, which was basically a rip-off of the S.U., that had a triangular air intake. This stopped the whistle, and Hudson started advertising the car as the "Silent Six".

Jon

Good tips. Will snug up the carb bolts and see what happens.

Otto, this does sound oddly similar to a turbo. Even the throttle position and which it “engages” is the same as a couple turbo vehicles I’ve driven.

That's hilarious, Jon.

My six is anything but silent. It ain't whistlin' Dixie, though!

Hudson's emblem is an inverted triangle. It's interesting that their carburetor had a triangular intake.

The big, spaceship-looking oil bath that was used on some 235 cars. What kind of noise was that thing designed to reduce?

Did you ever determine the source of the whistling?

I did not. I actually disassembled the carb and put back together, for a completely different reason. But I did make note snug everything up very well upon re-assembly

The carb base gasket was partially torn when I removed the carb. I’m doubtful that was the cause of the whistle, but it’s currently my best theory.

The carb is still sitting in my toolbox from many weeks ago. Have a rag plugging the manifold at present. Good reminder to get back on this thing.