Carburetor noise

Just like the exhaust port, the carburetor is a valve that is opened many times per minute, and an intermittent airflow passes through it at high speed. However, because the air passing through the carburetor is colder than the exhaust gases ( i.e. has a smaller volume, i.e. has a lower speed), the carburetor is only an important source of noise once the exhaust noise and propellor noise have been taken care of.

There are a couple of ways to reduce the carburetor noise :

use a carburetor muffler. The volume of the muffler only has to be approx 5 times the cilinder volume ( i.e. 50 cc for a 10 cc engine) because of the lower gas volume compared to the exhaust muffler. A simple air filter can have the same effect as a real carburetor muffler.

                         

reactive type carburetor muffler                                  air filter

cowl-in the carburetor. This is enough to reduce the intake noise to a level below the other noise sources in most cases where 10 cc engines and smaller are used. Note that it will become difficult to choke the engine when you start it.

           

partially and fully enclosed carburetor on some sport airplanes

use intake air from the fuselage : this is taking the cowling-in of the carburetor one step further. A tube is attached to the intake, and it is routed to a passage in the engine bulkhead. 

rear intake : easy to route the intake flow from the fuselage

Remarks : 

- This method can only be used in the case of large volume fuselages, where air can flow freely. Very often, sport designs in the 10cc class and smaller don't have a lot of space left in the fuel tank area.

- Some gasoline engines have rear-facing carburetors, which make things particularly easy when you want to use intake air from the fuselage. Glow engines of this construction ( see picture) are rare.