What can I do if I flood it?
If you've been trying to start your bike, cranking and cranking on the starter and it won't start, yet the battery still feels like it has plenty of power, then you may have flooded your carbs. In simple terms, flooding means you have too much gas and not enough air in your carburetors. This is quite often accompanied by a smell of gasoline, particularly the smell of unburnt gas in the exhaust.
If this sounds like your scenario, then try our member's steps, outlined below.
Recently I've had a problem with flooding my engine when it's cold. I've done it twice now at a stop light near my house. Very embarrassing. So, when I flooded it right in front of my dad, we had a good laugh (at my expense), and then he told me how to solve the problem in seconds, further reinforcing his claim to know everything about engines. *sigh* Anyway, for the benefit of other new riders out there, here's what he told me to do, along with a bit of explanation by me:
1) Turn the choke off completely. The choke (actually an enrichener circuit in the carb) dumps extra gasoline into the cylinder, so the mixture of fuel to air is a little higher and thus easier for the engine to burn. Gasoline does not burn by itself. It needs to be mixed with air first. The problem we're trying to solve is having so much fuel that the mixture won't even burn. It needs more air.
2) Twist the throttle open more than halfway. No, this isn't going to dump more fuel into the engine and make the problem worse. Twisting the throttle opens a valve in the carburetor to let more air in. As the air moves into the carb, it sucks fuel along with it. So, our immediate problem is too much fuel and not enough air. The throttle lets in more air, so open it up.
3) Hit the starter. The starter motor will turn the engine, causing it to suck on the carb, which will pull in lots of air with the throttle open, and the engine should start. But, yes, the air coming in through the carb will be mixed with even more fuel. So, if all this works and your engine really starts (it should) it will still have to burn off the excess fuel from being flooded, and it will have a lot more coming in from you having the throttle open. Expect it to rev really high.
4) Let off the throttle, but be cautious because if you let it out all the way, and your engine is cold, it might just die again. You probably had the choke on initially for a good reason, and you may need to turn it back on a little to keep a cold engine running.
For homework, Read: How a Carburetor Works (in the FAQ).