I have a 2002 Johnson J50PL4ST fuel injected 4 stroke. It runs great, EXCEPT for the first 5-7 minutes. When I first take it, out when it's cold, it will not go past 3000 rpm. When I try, it 'chugs' and I have to back off the throttle. After about 5-7 minutes of driving at 3000 rpm, I can move...