If you can get one the Lesiure not Enduro Yamaha 15 is I believe about 85 lbs, they are two stroke.
The lightest four stroke I know of is the Suzuki, and the 9.9, 15 and the 20 are all 99 lbs as they are all the same motor
, so if you go that route
Iíd recommend the 20 even if you donít need the power, itís there if you ever did, say to pull a boat
off of a sand bar or something.