I see that you adjusted the main to a 320 but what did you do the the pilot and the needle? the pilot should be increased by one or two sizes and the needle clip should have been richened by one or two clip positions. It sounds to me like you may have had a partial throttle sieze. I agree that you should be running a little more conservative fuel/oil mixture as the leanest I will run is 32:1 with my Klotz. Just remember that adding more oil will make your carb settings leaner as the oil will displace some of the gas. BTW....what color was your plug when you did a plug chop?