1976 Pontiac Firebird HARD SHIFT

16 BTDC for auto trans is the right timing. What is the engine idle? Poping up through the carb? Check for worn cam. You may have a vacuum leak, get a can of spray gumout, spray the vac lines and maniflod area, when the idle changes, youve found the leak! You want the engine running and spray on the outside but do direct the stream onto the hoses, if it is a vacuum leak, the engine idle will change speed, then you have detected a leak, repair the vacuum leak and see how it runs! Also these tend to carbon up the bottom area of the carb, pull the vacuum line off the back, you should get a strong suction there. If not use a piece of wire coathanger and with engine running clear out that port with the wire. Check EGR, could be rotted and lifting off the manifold.