I've wondered this rpm thing for years too. My old 200's would shift at 4500, and run past 5,000+. Now I have had two different 250's in the Maverick, and both won't hardly hit 3500, shifts at 3200 for second, 3000 for third. And the 250 has had both Carters on it, no difference. They seem to ET the same, 1/8 miles in the 11.15 @ 60 range. I have not juiced the 250 yet, my plate is for the 200 adapter, but it may go faster, being it has more low end. Maybe the bore/stroke combo makes the 250 not want to rev? I can't see only 50ci making that much more need for carburetion size. I tried that Clifford 2-1 with a motorcraft 2BBl about 15 years ago, no et gains, but it may help the 250. I have 460 in a 69 Mustang, so the Maverick performance is not real important right now, but my daughter will most likely race it next year when she quits driving Jr dragsters, so being her "little" Briggs can run 9.'s, she won't like running low 11.'s!