I got this classic, which is my first ever motorcycle. Today, when I tried to start it, it runs for a few seconds and dies. I took it around the block last night and it was spitting and sputtering. It started up just fine with the choke pulled out, but as soon as I push it in, it dies. Until it warms up, if I give it any throttle, it immediately dies. First obvious suspect is carb. It's very new. I have pulled it and it, and cleaned the jets several times. No apparent luck. Any ideas?