As my sign. says I run a truck avenger 670....secondaries are not opening early...........this is not a engine load problem...........enrichment is working properly.......I do not have Duraspark.........chain is a new steel double roller, timing mark is rock solid.......Motorcraft springs are on order. I want to tackle the distributor/timing side of this issue. At this point the carb has been dialed in and seems to be working well. Can anyone tell me the rpm/adv. curve for a stock '78 Motorcraft dist? At what rpm does it reach max. adv. I am hoping the adv. curve kit will solve this problem. Thanks to everyone for all of the quick responses.