Gee, I wonder what bike you have?
Anyway, pull the plug on number 1 and look at it and smell it, see if it is wet with gas.
If wet, lay the connected plug onto the engine, crank the engine over with ignition on to see if the plug sparks at the electrodes. If not, swap it with another plug to see if it sparks in either position.
If dry, and the plug exhibits sparking, then that cylinder's carb is suspect. See if the bowl is filling with gas.
Is the tank internal and the fuel clean?
Let us know what you find and we can take you to the next step of the either ignition or carburation troubleshooting branch.