Thanks for these answers to your post! I just ran a can of Seafoam thru the carb on my 70 383 mag & whatta difference. The 383 sat on a stand for 7 yrs before the install in my 71 Power Wagon & had a big cam that didn't help matters. Low stall verter & tall 35" tires w/ 3.55's got the motor loaded up w/ carbon & suit for the past 8 mos. Poured 1/2 of the can down the carb @ 2000 rpm & then dumped enough to stall it. Let it sit for 15 minutes & fired it up. Smoked big time for a minute & then cleared right up. Truck runs much better & can notice more low end throttle response & smoother idle. Gonna switch the cam soon, but this was a good fix until then. Also put the last 1/4 in the tank.
BTW, I did put some Marvel mystery oil in the plug holes before the install to lube things up, but that was months ago. I also heard Marvel Mystery oil is good for a top end cleaner, too??