XS,
I don't have as much experience as the other guys on this site, but have been hitting it pretty hard in terms of research on this topic. The common theme I've heard from people on this site and other places is "don't underpower". In your case I'm assuming you're looking at the Yamaha 40, 4-stroke jet. It's my understanding that this motor produces approximately 28 hp at the pump. Nothing against 4-strokes, but for a jet pump I've heard a 2-stroke is preferable because it winds up/produces power more quickly than a 4-stroke which translates to better hole-shot. Your boat sounds like it is fairly light so don't know if this will matter as much. If I were you, I'd be more concerned about the weight issue. How well does your boat ride with you and a 200 lb motor in the back? One other thing to consider is the height of your transom. You will probably have to increase it's height to somewhere around 27" via an engine jack or transom extention.

When I did my research I spoke with the folks at Wooldridge who have forgotten more about this topic than I will ever know. They in turn gave me the number for the folks at Specialty Manufacturing (the guys who make the outboard jet units). Specialty has a brochure that helps with selecting the right size engine for a boat based on weight. Between Wooldridge and Specialty Manufacturing I got almost all my questions answered.

I don't have Wooldridge's number, but they are on the web. Shoot me an email if you want to discuss further (jsullivan@kennedyusa.com)

JMS