How long have you had the YF2100? Not miles, but length of time.
The accelerator pump diaphragm does not get along at all with today's formula of gas. They develop pinholes and cause significant flooding just as you are describing. I get 1.5 to 3 years out of mine before I have to replace the diaphragm.
Pull your plugs and see if they are covered with black soot.
Perform the tests mentioned above.
If those tests don't indicate problems and the spark plugs are sooty and the carb has not been rebuilt for a long while, rebuild it.
Like I always say, "Its always the carburetor."
Actually I never say that, but it might be the problem in your case, since you are going to check out everything else first.
What I should always say is, "You should always check out everything else before you dig into the carburetor." But that takes too long to type.
Carl
