I stacked mine and on the first test pull I let off in second and removed the pulley. AFR's at WOT in the 14's. Got a retune and SL55 pierburg and tried again. It was still lean at the top of 3rd. but now around 13 AFR. I ran my car anyway at the track but had a tank full of 100 octane. I wouldn't even try stacking the pulleys without doing some supporting fuel mods beforehand. It's just too risky, and a risk several of us have taken and later concluded, "that was dumb!"

Les