My '73 Z (L28, '72 SU's) seems to be in need of a tuneup. It's run great for the last year, but increasingly, it runs better with the choke open. Even warmed up, it frequently seems to bog down with the choke closed. It's been 10,000 miles since the valves and points were adjusted at the shop. What are the symptoms of a car that needs valve/points attention? Or is this more likely a carb thing? Thanks for any help!