1. Is the backplate sealed? If not, do that! I'm about to do that myself, as a precaution. I'm not having probs yet, but it's good practice.
2. How did you check the carb? Did you dunk it in water and blow air? It won't show leaking fuel, and won't make a hissing sound or anything when you blow in it. Dunk it for sure, put your fingers over the two big openings, and blow in the fuel line.
3. At race temp do you have bubbles in the fuel line at carb inlet? To check, warm it up with body off to where it starts bogging, bring it in and inspect closely. If I route my fuel line around the motor like stock that happens to me. I think it's a combo of heat and vibration from motor. I rerouted my line and bubbles disappeared. Some pictures of CRT's show other people rerouting too, and I have to assume they had the same problems.
4. If it's just breaking in, what temp was it on the track? It still has pinch, so it could overheat easily. If temp was high, did you richen HSN or just LSN? I'm guessing that with the JP1 you are on a very tight track. I think you could keep good punch and temps by running a normal LSN, not too rich, and richening the HSN to give more cooling when at high RPM. Performance tuning should be done at full temp. If it's running like lightning on the first lap without any warmup, you may be running lean on one or both needles. Since you have experience tuning obviously, check the stuff above first and make sure nothing wierd is working against you.