I have a bone stock 305 in my 85 Chevy pickup and I just installed a reman Q-jet on it. Anyway, it works great except when you bring the truck to a stop. During the slow down, everything is fine, but during the last second or two of the stop and for about 10 seconds after the stop (when the truck is sitting still), the motor will barely idle. After about 10 seconds or so, the idle comes back up and is very smooth.

I'm usually pretty decent with a Q-jet, but this one has me baffled. The idle mixture is set correctly. I am thinking that there could be a problem with the float? Any ideas?

Is it usually cold or humid out when this happens? Do you have the thermostatic air cleaner working properly?

My '86 C10 did the exact thing, and I found it was carb icing. The super small primaries on those things speed up the airflow so much, ice starts to form. After a while it would melt away and the truck would run great.

No, it does it all the time, no matter if what the weather is. Engine temperature doesn't make a difference either. It has the problem when it is cold and when it is warm. I am really leaning toward an excessively low or excessively high float setting. That's the only thing that I can think of that would cause this problem. But, I am open to suggestions, if anyone else has one.

Is it a computer-controlled Q-jet?
Are the bottom plugs leaking?
Sticky throttle plates?
Return spring too strong?
Missing dashpot?
Have you disconnected other vacuum hoses to other accessories and retry?
Swapped another carb just to compare?
Vacuum advance being brought into retard with closed throttle vacuum?

is the lockup torque converter unlocking?

The torque converter is unlocking. It wasn't at first though. I had to unplug the vacuum switch that controls it. I was hoping that would fix the problem, but it didn't.

I did notice yesterday that when the truck is stopped and pointing downhill, the idle won't ever smooth out, which makes me think even more that it is the float.

See if you can make it idle rough again (point the nose downhill, maybe on jackstands?) and look down the venturiis to see if you can see dripping fuel.

Matt,
Good idea. I'll give that a try as soon as I can get a chance.