I used to belong to a forum for another car, and the resident carb guru had a saying: "90 percent of carb problems are timing problems." I had what I thought was a fuel problem. I went as far as swapping carbs, but it turned out to be an ignition problem after all. Just a thought.....
Jerry
X2 Timing at 15 sounds low with that car. don't know how your engine is built mine is set around 30
__________________
Ray
1970 SS Chevelle Van Nuys Built