ATV has about 30 hours on it… don’t run it much turn it on every once in a while

Problem:

I recently replaced the battery on the atv, went out riding and now it just tops at 20mph, i try to accelerate and it starts making loud popping noise.
Nothing else is wrong… 4×4 engages and disengages, turns on normal

I am pretty sure it is a simple fix.. any one had this issue before?