IN a Buggy the mod JPX 21 would likely spank a stock OS 28.... you could;d gear the OS 28 way up to get better top speed, but then you lose all the bottom end advantage...in a light vehicle like a Buggy the mod 21 is going to be nearly impossible to beat... I own a OS 28 and in the buggy its no match for the mod JPX ....

As for tuning, JPX tune easy, very easy...especially if you run Picco plugs.....I actually prefer tuning my Picco's over my OS, I find the carbs more precise and more accurate to needle changes... They have a very distinct sweet spot, whereas the OS is kind of obtuse and doesn't always respond to small needle changes...