Ok, the older carbs with the venturi had a good sized bore. Maybe about the same as a TT .46. I think someone said the carb was change about a year ago. Not that they knew it was changed a year ago, just that they had one with a smaller bore and they reported this about a year ago. Mine is about 4 yeas old and has the large bore carb. With the venturi they are very reliable with lots of power. However, because of the large carb and venturi they do not have a liner response. Most people do not know this but the reason four strokes have more controlability on throttle is because of the smaller carb. The TT .91 FS is actually worse about this than any engine I have had including all two strokes. There is almost no differance in power from 3/4 throttle to full open, in fact I think it runs better if you don't fully open the carb.