Crusty is correct that there have been more than a few KR's built too heavy to fly, or fly safely. However, many are flying that weigh in the 550-600 lb. empty range. Mine is one--- weighs 600. I have had several flights with 300 lbs of humans & 60 lbs of fuel, with no problem. Climbs 1000 fpm, 100 mph, at that weight. The CG on my KR is very near the aft limit with 2 people & low fuel, but within spec. This is with a 2180cc 75hp engine. If yours has a 1600 or 1800cc engine, you would want that bird to be nearer the 450-500 range.