Big Features

I recently replaced the water pump and removed the intake manifold to paint it. I discovered lots of sludge and build up. I removed that, painted everything and put it all back together. Not under acceleration, there is a sucking sound under the hood. All vacuum lines are connected and I used Edelbrock intake gaskets and ULTRA Copper for end seals. We sat the manifold on the block perfectly with no wiggling; everything lined up. Car goes like stink at full throttle, no oil/water mixing, and no leaks. I even sprayed carb cleaner at the base to check for a leak around the manifold and carb. Any thoughts?

oldcutlass

Have you hooked a vacuum gauge up?

MDchanic

Any changes to your carburetor or air cleaner?

- Eric

lemoldsnut

double check vacuum line to booster. had one look in but was really not and it would make strange noise. Check other end of all vacuum lines as well.

Yellowstatue

On the manifold, ahead of the throttle linkage, there are two holes for the dash pot to mount. One hole (threaded) goes into the intake passage.

Big Features

how much vacuum is my stock 400 supposed to have?

Big Features

replaced the stock unit for a k&n 14" open air ckesner. I placed a push-in style breather in the driver side and PCV valve to 3/8 inlet in front of q-jet

Big Features

all good

MDchanic

At the same time as the rest of these changes?

- Eric

Big Features

yes.

MDchanic

It's your carburetor. They all do that.

You just can't hear it with the stock air cleaner on, because it's designed to muffle the noise.

When I worked for NYC*EMS "back in the day," we used to flip the air cleaner covers, because the giant air rushing noise would scare the pedestrians out of the way more effectively than the siren, which they were used to and ignored.

- Eric

oldcutlass

I bet when you floor it you hear the secondaries kick in loudly also. As Eric stated the noise you hear is normal with an open air cleaner.

TripDeuces

Oil fill tube. Did you remove and block off the PCV system by chance?

Big Features

pcv system is hooked up, don't think it's the oil fill tube. It's coming from the carb at partial throttle under load

TripDeuces

Have tried driving it without the air cleaner assembly to see if that's it and not the carb? Be careful of the under hood insulation if you have it

oldcutlass

Do you have the original closed air cleaner assy? Install it and see if your noise goes away.

MDchanic

+1.