I recently purchased a 60s model evinrude 80hp. The motor starts right up with no problems and runs very smoothly when testing. I took it out to the lake for it's first test drive and it will go into gear, but when put in forward it seems to crawl. It will not plane out and goes very SLOW. When put in reverse it runs great and when in neutral it revs great. Anyone have any idea what could be causing this problem?