How to Fix a Carburetor Vacuum Leak

On carbureted engines, vacuum pressure is created by the operation of the engine to pull in fuel and air through the carburetor. If there are any leaks in the system, the air-fuel ratio will be disrupted, and the engine will not run properly. The first step is to find where the leak is coming from. Then you can replace the gasket or seal that is allowing air to enter the engine system. Using some common materials, you can find and repair vacuum leaks yourself. This technique will work on any carbureted engine.

Instructions

1

Start the engine and let it attain a steady idle. This may be difficult depending on the size of the leak. You may have to run the engine at a higher speed. Find a level of rpm's where the engine stabilizes and does not increase or decrease in operating speed. Have a friend hold it at this level.

2

Spray some starter fluid in short bursts around the mating surfaces of the carburetor and engine, air filter and any other rubber- or gasket-sealed surfaces.

3

Listen and look for any increases in engine speed. If the engine increases in speed, it is due to the starter fluid being sucked into the system and combusting. This is a sign of a leak. Take note of this location and move on to others.

4

Replace or repair any rubber, gaskets, or seals in, on, or mounted to the carburetor where an acceleration in engine speed was noted in Step 3. If there is a crack in the carburetor body itself, it will need to be replaced. Tolerances inside the carburetor need to be exactly as they are designed, so cracks cannot be filled.