Quote Originally Posted by csbuckn View Post
Fuel is another good place to look along with timing. Wires ran correctly or something being pinched by a valve cover. Almost sounds like the advance is not working correctly. Not sure how the dizzy advances with the CCCarbs but it would run good with no load and run bad under load if the advance werent working correctly. Cap on nice and tight?
The 307 has electronically advanced timing, based on calculations in the car's computer.

The distributor cap has two electrical connectors at the bottom of it. During a tune-up, it would be very easy to pull one of them loose, and cause the distributor to revert to base timing; without the advance timing, the engine would have trouble at driving speeds. So that is something to be checked into.