I have a Yamaha 350 and when I try to start it the engine just turns and turns but it doesn't start. Battery is new, the spark plug is clean/dry and new, and fresh gas. I cleaned up the carb also the other day. I have held the choke open while giving it gas, but it just turns. When ever I hook it up to my car battery after a few seconds it always starts, then it runs fine. After warming up it starts up right away. Any one have any idea what the problem could be? Would changing the oil make a difference. Thank you.