Vacuum Leak Carburetor Symptoms. Normal vacuum for an engine at idle runs at 14 to 18 inches of mercury when measured with a gauge. When driving with a leak, you can notice symptoms such as abnormal idling speeds, rough idle, hard braking and poor fuel efficiency, and many others.
When driving with a leak, you can notice symptoms such as abnormal idling speeds, rough idle, hard braking and poor fuel efficiency, and many others. One of the vacuum leak's signature symptoms is that it seems to go away under full throttle conditions, particularly at high rpm. A fuel leak from the carburetor will also disturb the air to fuel ratio because it’s going elsewhere.
