Originally Posted by
Dammit!
I think everybody is over thinking this. Billy, if you're asking what I think you are, I believe you're right.
If two 250Rs that are more or less the same mod wise and are running the same carb but one has a bigger main jet (and assuming they're both jetted right... one just needed the bigger jet to get the right mixture) the one with the bigger main is going to be making more power most of the time. It won't be accurate 100% of the time but I think it would usually be a safe bet. That's been my experience with 250R's anyway.
Now if we're talking about two radically different motors with different strokes and displacements, obviously there's too many factors involved and you can throw it all out the window.