Originally Posted by
Rocket42
To pressure test the carb. remove the carb from the engine and clean it up, Get some fresh fuel tubing about 6" and a dish of water. Put the fuel line on the fuel nipple. Dunk the carb into the water with your index finger and thumb covering the openings, and blow into the fuel line. You should see your throttle body pushing out and if you see any airbubbles then you know you have a leak.
Believe it or not but a carb can still pass this pressure test yet still have an air leak when installed on the motor.....It seems the metals in the carb can expand when it gets heat soaked and cause a air leak that will only appear when the carb is up to engine operating temps... The motor will tune and act perfectly for approximately 1 tank of fuel, after that a phantom airleak will apear as the metals in the crab get heat soaked.......
If in doupt seal the carb, testing for airleaks when the carb is cold will only tell part of the story....as the tolerances int he carb changes quite a bit as it gets up to operating temps....I have had several engines that were airtight when cold, but started leaking once they got hot... Always the same place, the seem between the metal end cap and the composite carb body