I just recently purchased a 1980 overnighter with an original 175 mercury on it. The boat and engine seem in pretty good shape. I brought it out the first time yesterday and was having trouble getting it on plane. It seemed that i had to get it to about 6k rpms and once i let off a little i would loose too much speed and loose it. My last and only other boat was an 18 foot baylner that easily got on plane in seconds. Is this normal?