Thanks for tutorial, will take awhile for me to "absorb" this.Yes impulse port. It is what operates the carburetor's fuel internal pump. If no impulse then no fuel is pump through the carburetor.
Here a tutorial on these.
Walbro Carburetors - So how does this thing work - HeliFreak
This thread is going to cover the internals of the Walbro carburetor that almost all gas helicopter engines use. Specifically the ones found on thewww.helifreak.com