misfire while maintaining speed

70 duster 318 edelbrock 4 barrel factory dizzy with points.
i just removed the distribtor to clean due to siezed adv. weights
wile cleaning i found that at one point the weights would stick.
after thinking i had fixed that issue, i reinstalled and now wile driving under load
no missfire but when holding the throttle to maintain speed i get a muli misfire.
once i step on it it goes away. thoughts?