And when you guys say, lightly modified engine, im not much of a gearhead, so i dont know how to do that kind of stuff.
Oops! Sorry about that. Just like we all have differing opinions on all things, my definition of "lightly modified" involves a trip to the hardware store for the B/S 5hp motor. There's an article I copied and posted somewhere under the engines section about someone step-by-step modifying and testing a B/S 5hp engine.
They found that the biggest (and cheapest ) gain was modifying the exhaust and readjusting the carb mixture. The stock muffler can go away, and about a 14"- 16" pipes screws into the block in it's place. (Costs about $3). Then you readjust your carb mixture by a screw on the side for best performance. You WILL feel a difference, as even within the stock operating rpm, gains were there.
Now, if a straight pipe is too loud, you go get a B/S muffler for the 8hp engine. (It has more flow and a larger fitting) The muffler is about $9, and the pipe adapter (goes on the end of your straight pipe) costs about $2.50. The warning here is, that much weight sticking out of the exhaust port will eventually strip the threads in the port. Find a way to brace the end of the pipe so it isn't all held up by the part that screws into your engine. If you can't come up with a way to brace it, you can "split the difference" in performance by getting an plumbing adapter that goes from the motor's exhaust port size to the size of the 8hp muffler, and bypass the long pipe. I've tried this set-up, and it's better than stock, but not as good as with the long pipe in there.
On the 6.5hp Clones, there are (relatively) inexpensive kits available on Ebay, that include a header/muffler and replacement jets for the carb. (No clue as to what the actual hp gains are). When the dust settles around the other projects I have going, I'm going to purchase one of those kits and try it out on one of my Clones.
Going back to your original post in this thread and your weight, a HF 6.5hp Clone will have you scooting quickly!