I recently bought a 1981 SR250. After the first day of driving it around all the sudden sometimes when you roll on the throttle it just kind of sputters or doesn´t really change anything. After waiting for about 30 seconds it hits as soon as you roll on it like normal again. I changed the air-filter, spark plug, took off the tank and cleaned rust out, (maybe not perfect though) made sure the pet-cock was letting gas through, checked hose from gas tank, and it is still doing it sometimes... Today, pretty much it was running fine, then after about 10 minutes I was sitting at a stop sign and it was my turn to go. I hit the throttle and nothing, hit it nothing.. walked my bike to the curb and sat for a minute turning the throttle and after about 30 seconds it was hitting spot on perfect again! Maybe it´s a carb problem?? Any thoughts and advice would be greatly appreciated!