250 running badly.

[brian.kannady]

So I finally got my 67 with a 250 and 3 on the tree out today. I managed to keep things from breaking too catastrophically to keep running long enough to get out of the driveway. The engine runs fine in the yard (minor stumbling on initial acceleration) and revs just fine. On the road, however, it was almost undrivable. At WOT it stumbled really badly and got worse the longer it went, and by the time I got it turned around and headed back home it would only run with the choke fully out. I only managed to get about a mile on it. After I got it back in the yard, it was OK again. It is all stock except for the HEI conversion. It has a brand new fuel pump, new fuel filter, the HEI is brand new, the carb is a fresh reman. Has plenty of fuel in it. Timing is 4 degrees before just like the manual says, I have spark on all six cylinders. The idle speed screw is 1.5 out as the manual indicates for a starting point. I checked and there is plenty of fuel to the carb.

Any thoughts?