Oil in the vacuum advance canister and tube

Texasdoc · #1 (**permalink**) 05-27-2014, 12:33 PM

Here is one I can't figure out.

351W with MSD 8478 distributor. Swapped the vacuum advance canister for an adjustable one. Works fine. Vacuum line is connected to the manifold vacuum port on the bottom of the carburetor. While recently trying to figure out why the engine runs rough, I disconnected the vacuum line where it attaches to the canister. I noticed that there is oil in the vacuum line. I'm not sure where it is coming from.

Only thing I can think of is that it is coming up from the valves (or down thru the valve stems from the heads), and going back up to the carburetor. Although I don't see any oil when I take off the carb.

I do have a PCV valve connected to the main vacuum port on the back of the carb, but there is a catch can in the middle of that line, and it stays bone dry. Plus, this comes into the carb in the back by the secondaries. It would have to go down into the intake, then back up by the primaries, then thru the small hole that provides the source for the vacuum port.

The inside of the distributor is clean. I just don't get it.

Gaz64 · #2 (**permalink**) 06-03-2014, 03:09 AM

You have oil in your intake from leaking inlet valve seals, leaking inlet manifold or high blow-by.
The vacuum canister when it retards the timing pulls oil into the line and canister over time.

It may be only residue but builds up to the oil you see. How much are you seeing in the line?

Texasdoc · #3 (**permalink**) 06-04-2014, 06:53 PM

Not seeing a ton, only a few cc's. However, it is there. I pulled the carb yesterday and noted there was a small amount of oil in one side of the intake. Now I gotta figure out where that's coming from.

Definately not seeing any white smoke in the exhaust. I'll pull the plugs and see what comes out.

Gaz64 · #4 (**permalink**) 06-05-2014, 12:43 AM

Quote:

Originally Posted by Texasdoc

Not seeing a ton, only a few cc's. However, it is there. I pulled the carb yesterday and noted there was a small amount of oil in one side of the intake. Now I gotta figure out where that's coming from.

Definately not seeing any white smoke in the exhaust. I'll pull the plugs and see what comes out.

Sounds like intake manifold gasket on one side.
Manifold mismatch to angle of heads.

Jac Mac · #5 (**permalink**) 06-05-2014, 12:58 AM

Are you using the vac advance for cruise or idle, sounds like your using manifold vac rather than throttle plate/ported vac which might be close to the discharge area of the idle / progression slots. Still doesn't explain the oil in the line though since vac from manifold should tend to clear any of that.

Texasdoc · #6 (**permalink**) 06-05-2014, 09:12 AM

Yes, manifold vacuum. Guess one of these days I'm gonna have to pull the intake.

Jac Mac · #7 (**permalink**) 06-13-2014, 03:37 PM

Quote:

Originally Posted by Texasdoc

Yes, manifold vacuum. Guess one of these days I'm gonna have to pull the intake.

I would try shifting that manifold vac source to a 'drier' area of the intake manifold, I think that when you switch the engine off the vac advance unit which has 'high' manifold vac at idle pulls a bit of rich idle fuel mix back in as it returns to a no advance position simply because the current vac source is close to the idle fuel slot.