2000 70hp Johnson outboard problem

by Jono
(Magnetic Is. QLD Australia)

2000 70hp Johnson. starts fine, idles fine, accelerates to full speed fine after 2 min it looses power. If i
back right off to where all cylinders are firering i am now only just plaining. Then if i let it sit for a while it gets to full speed then same problem. I hive bypassed fuel filter to check , same problem.