Once trimmed, and with the butt tenderloin (the lobe at the large end of the roast) still attached, the roast should weigh 4 1/2 to 5 pounds. If you purchase an already-trimmed tenderloin without the butt tenderloin attached, begin checking for doneness about 5 minutes early. If you prefer your tenderloin without a smoky flavor, you may opt not to use wood chips or chunks.