I have an old 340 that the kids are learning on it runs great at 1000 ft. And jetted for that when I jet it for 6000 ft. and take it to the Black hills it runs fine for about 15 miles then It gets really doggy and then wont turn the track, let it sit for 20 min and it is good for about 10 miles then acts up. Any ideas on what to look for or try to fix the issue. Kids aren't ready for a 550 yet. One is 7 and the other 2 are 4.