Tex, Jerry has given you the right answer above. If I were you, I'd get an original intake/exhaust manifold and the Carter YF one barrel carburetor engineered specifically for the 250. I think it would be the YF 4339S, although there may be others. When you stop to think about it, the 250 is 15 cubic inches larger than the 235. 15 cubic inches is approximately the volume of a cup of water, and that isn't much. With the 250 your net torque maxes at 185 at 1600 rpm and your net horsepower maxes at 110 at 3800 rpm. That's pretty nice, but it isn't a high performance engine by anyone's measure. If you want to see your torque/horsepower curve, go to this page and follow down to page 31:
https://www.gmheritagecenter.com/do...hevrolet-Trucks/1972-Chevrolet-Truck.pdfJerry may disagree, but what I've seen is too much carburetor will make an engine run rich and wonky at idle and off-idle. You can adjust the idle mix with the idle mixture screw, but you can't adjust the off-idle performance. It is built in with holes drilled in the throttle body or through a vertical slot cut in the throttle body and this off-idle zone is meant to offer a smoother transition from idle to driving speed so you don't fall off into a dead zone pulling away from a stop sign. So, when you pass the off-idle rpm spot, your engine begins running leaner (as more air passes through the venturi) and it continues to get leaner the more you open the throttle. When it starts running leaner, it starts stumbling, stalling, popping, even backfiring in some cases. Bottom line...it doesn't run well at all (with good reason). And if you want to read about off-idle stumbling, go to Google. Type in off-idle stumbling and see what you find there. I did that early this morning and got over 6,000,000 hits. You want your carburetor balanced from curb (some call it driveway) idle all the way to full out open. If you don't have that, you basically have a mismatch and you won't be happy with it. If I could offer any advice at all, it would be two things: any engine will ALWAYS run better with too small of a carburetor than with too large of a carburetor and any engine will run better with a carburetor designed specifically for that engine. Good luck.
