I bought the 1406 carb new in 2012 for use on a 1989 Jeep Grand Wagoneer. Never used it on that, so i threw it on my truck. Has run like crap since. I finally found out why: That carb is tuned for fuel economy only, which leaves it running a super lean fuel to air ratio. It has no top end power and stumbles when you punch it. I have had it tuned before with no luck. Today I put Lucas oil treatment in the oil, which brought oil pressure up 10psi then adjust the fuel accelerator pump thing, and put an octane booster in the gas just to see what happened. The octane booster seems to have helped a little, but adjusting the fuel pump on the carb helped it alot. I will be following this guide asap.

1406 Tuning Guide