Hi, no. They are manufactured to the correct mixture. If it's not running correctly it will need a thorough clean. I have cleaned them several times. Some just needed a rinse whilst older ones needed a good scrub inside. The main/only issue is the tiny injector. The nut on the bottom of the carb is the injector on Tecumseh models whilst the nut reveals the jet on Delorto models. A small splinter of wood will clean the jet. Don't use anything else as it will alter the jet.
Hope it helps.
MowerMan, August 2011
