I've got a walbro carb that has given me a small problem since I got it. After I start it, it runs great and has great power and transition. After the flight, if the plane sits for more than 5 minutes, it will start immediately but hesitates and runs unreliably for about a minute. Then no matter what I do, it quits. I have to choke the engine to get it to start again. Then, after it restarts, it runs fine. It happens every time. The line stays filled with fuel all the time. Any ideas? Thanks.