Back when I was a GM technician we would use GM Top Engine Cleaner. Now I just use transmission fluid. Get yourself a squirt bottle fill it with about 8oz or so, get the engine warm,shut it down remove the air cleaner, start the engine hold the engine at about 1800 rpm, fast idle and start to squirt the transmission fluid down the air horn of the carburetor SLOWLY. It will smoke badly, keep the idle up about 1800 or so it will want to die, after you get most to all of the fluid down the air horn let the engine die. Turn off the ignition switch. Let it set,the longer the better. Overnight would work. The transmission fluid will soften the deposits on the valves and in the cylinders. Put the air cleaner back on, start the engine keep the idle at about 1800 rpm, it will blow a lot of smoke. Go for a quick run until the smoke clears. Your neighbors and the cars behind you will hate you. Then change the engine oil. Then after that put about 8 oz or so of transmission fluid in your gas tank when you fill up. After awhile you can put transmission fluid in your gas tank when you think of it. Hope this helps.