I bought a used 05 YZ450F recently that had sat for two years with fuel in carb. I got it to run great after draining the fuel and putting fresh gas in it, though it wouldn't run unless the choke was on. I decided to pull the carb and inspect the jets. I found crud in the float bowl and gave the jets a good cleaning with carb spray and compressed air. I gave the vent passages the same spray and air treatment, put the whole thing back together. It starts easier, first or second kick, but it dies immediately if I push the choke in. If I let it warm up I can start it by pulling in the hot start trigger with the choke off, but I have to hold the hot start on in order for the thing to run. As soon as I release the trigger it dies. Any body have any ideas? Also, what is that little electronic switch on the left side of the carb? It appears to be some sort of throttle position sensor, but I cant figgure out why a carburetted bike would need that. Thanks in advance!