As a number of other posters have stated the problem is in the choke. When you close the throttle all the way it will pull the fuel through the idle circuit at cranking speed and start. You need to take a look at the choke butterfly and make sure it is closing all of the way so it seals off almost all of the air. Also some engines have holes in the butterfly so the engine will not completely flood out with full choke.I have seen cases where these holes need to be partially or completely plugged off so the engine would start under some conditions.....usually when the engine is used in applications with high parasitic loads that result in slow cranking speeds.