4 strokes and weight

I have been looking around boat stores in the area for a used 25 hp engine to be able to swap off and on to my boat depending on what lake im going to. Some of our lakes are 10HP restricted while others are not. So in looking at used 25s I have come to appreciate the incredible weight of 4 stroke engines. For instance, yesterday I looked at 2 mercs..both 25hp and both 4 strokes. They were made in 2003 and 2004. One weighed 180 pounds and the other one 172 pounds! So in no way can I go with either one of these because I can physically lift them. I came home and got on the web and was doing some research on lightweight 25HP engines. I found that Yamaha 2 stokes weigh a mere 105 pounds! Thats 75 to 80 pounds LESS than the 4 strokes I looked at! Needless to say Im now in the market for a 2 stroke Yamaha.