Seafoam worked on one car but nothing on other

Well I seafoamed my 70,000 mile 2000 GT. Decent smoke show, seen better ones in videos from here. I also Seafoamed my 85 5.0 with 210,000 miles. All I got was a little puff of smoke when I restarted it. I even went and bought another can since first attempt I just poured it down the carb. Second try I did like on my 00 and sucked it up through the PVC. This thing shoulda smoked out the whole block. I read the instructions... sucked up nearly half the can and turned it off for over 5 minutes and restarted. What gives??