Vacuum leak?

[mpi115]

Hello, I did the old novice test of taking off oil cap, while engine idling. And the car did seem to bog down a little. Maybe a change in rpms from 1000 to 900..ideas ?

[stlrj]

It is quite possible that your mixture is just right, causing that to happen. But the only way I know how to check for vacuum leaks is to spray carb cleaner where you suspect a leak and see if the idle goes up.

[mreid]

Isn't that what it's supposed to do?

[DRACO A5OG]

To answer your post tile, YES. you introduced a vacuum leak by opening the oil filler cap.

Is that idle when the car is warm or at start up?

BTW, it is normal for the idle to drop when you remove the oil cap. If it did not drop in idle then you have a vacuum leak.

[Bob Kontak]

You are fine as noted. SC correct?

You may have little leaks, many of us do.

If you want to test for vacuum leaks turn the air-bypass screw in gently until it hits bottom. Your engine should die or be barely running. If it does not act starved, you may have a vacuum leak as the leak is providing air to allow the engine to idle when the throttle plate is closed.

Just count the turns in to get you back close to the starting point then tweak the rpm using the tach.