i whole heartily disagree with the pre-cross flow comment.
when i slapped the weber (32/36) on my 18r the power increase was extremely noticeable, feels as fast as the gt familia i had which was 109hp and the 18r startd out at just under 90. at a guess it was easily over 10hp for $50, opened up my rev range an extra 1500rpm and made it a whole lot more slipery in the wet!
i did do alot of research and knew the 32/36 was going to be a worthy upgrade as it was quite well matched. but i think if you can do alot of the work yourself, it can be quite cheap and quite enjoyable to play with.