its always good to use fresh fuel. 3 weeks in the can is fine as long as you always tightly close the cap. 3 weeks in a fuel bottle not so good. See, the fuel wants to suck all the moisture out of the air, keep it closed to keep it fresh.
Is your hesitation/boog happening after you idle for a few secs or every time u open up. Also does temp make any diffrence I/O does it change from cold to hot? Does it die out? 1 more, is this the trx2.5 motor?