^^^ sounds like tire and throttle issue.
Most tracks I've been to, as you progress thru the day or night the track conditions do and can change. Like mentioned what worked earlier in the first round might not later. I usually have 2 or 3 sets of tires.
I just recently got into the 2w buggy class and one thing a lot of the guys at track told me was if your going to you your brakes a lot to turn them down so you don't lock up and spin out. The most I use my brakes for is mainly if it's a big double or step down to drop the nose a little.