I have encountered a random but nasty lag in throttle response recently. I believe it could be the air valve on my 1405. If I start the car in park with the air cleaner off and watch the valve, it only opens up "sometimes" when I rev the motor. Anyone else ever hear of this problem? I didnt have a tach to watch while I rev'd it but I would guess I was revving it up to 4,000 or so.

You'll probably not see it open revving up in neutral. The air demand is too low to open it. Make sure the idle mixture is correct then try different holes on the accelerator pump linkage.