[zac]

If the truck is off, the power piston should pop back up freely as there is a spring under it. If it doesn't or seems kind of sticky, you may have found the problem. A little carb cleaner down there probably won't really hurt, but it shouldn't be considered a fix. It would still need a rebuild. When the truck is running at idle, the piston should be down all the way. At high vacuum, the piston keeps the fat part of the metering rods all the way down in the jets. They come up to expose the thinner tips of the rods as vacuum drops under acceleration to richen the mixture. My idea is that maybe they are stuck in this richer condition, although this may not really be a factor at true idle.

Check to see if you have Q-jet nozzle drip. At idle, no fuel should be dripping out of the nozzles in the primaries at all. But many times it does because the curb idle screw has been turned up because you have a bigger than stock cam. Also, large displacement engines will have this problem because they require relatively more air at idle. The Q-jet booster rings are so efficient that any air flow through them can cause the nozzles to drip, which can give you rough idle and a seemingly rich condition. This is why Rochester developed "idle bypass" for some carbs which will allow an engine to idle perfectly with the butterflies completely closed. It's why I use old Caddy carbs exclusively.

People have mentioned float level as well. Either way, sounds like you need a rebuild. Take your time. If you spend a little time reading up on how these things work, it makes alot more sense.