It calls for 91 FS engine but the plane will come out around 26-29lbs. some of the really early models came in around 23 lbs but most all that have been there hasnt been one under 25 lbs. some have been around 31 lbs. Most guys are putting zenoah 26's in them some have installed ZDZ 40's. With the 91fs engine the plane needs about 5-6 lbs of nose weight.