I have a 1980 D150 that burned and I am just now about to finish rebuilding it. Before it burned, it had a 1BBL Carb. and would easily get up to highway speed and a little more w/out an overdrive gear. When I started to rebuild the engine, I found a 2BBL manifold that a friend had. He was using the original carb. so of course i bought a rebuilt one. The engine runs and idles fine but I was taking down a country road in 4th gear, pedal to the floor and only going a little over 45 mph. Is the engine not getting an even mixture to all 6 cylinders?

Hello and welcome! You are right to suspect the carb. I am assuming that the carb is a Carter BBD since that was the most common carb used on the Super Six (the factory two barrel option). Reman carbs are almost NEVER correctly adjusted when they come out of the box. This is where I would start. Take the carb back off the engine and adjust it to correct speck. You will have to do all the adjustments (float, choke, metering rods, choke pulloff, idle, etc..). I also would make sure that your valves were adjusted correctly and that you have at least 10 degrees static advance in your timing. If those don't fix your lack of power I would suspect a vacuum leak or a faulty lean burn/ spark control computer.

Reed

Reed got the good points.

Another thing to consider is which tranny your truck has...

Is it the Overdrive 4 speed or is it the 'straight box'....

If it's the OD box, shifting into OD under 55 mph in the truck pretty much kills any power the slant has....even my stock drivetrain with the OD and 1 barrel necessitated a shift at that point to keep the thing from being a slug and bogging out/luggin hard when going to OD....

Check the carb, try shifting a bit higher on the tach/speedo/whine-by-ear.

Do you know what your rear gear ratio is? Hopefully it's in the 3.55+ range.

-D.Idiot