I'm working on the Merc with a 312 and 3 speed automatic (P R N D L). The owner says he can outrun this car for the first 100 yds. We checked the timing, 6 BTDC. We checked the compression. Ranged from 125 to 150 about a 50/50 split, so not at the best. He uses leaded gas, not sure about the octane. We adjusted the single 4 bbl carb. This engine fires right up, runs smoothly, sounds great. Shift into gear and the torque converter engages solidly (bumps the car forward if the rpms are a little high). This car is stock, other than the air filter. The owner recalls from youth that these cars had more guts that what he's seeing.

So any suggestions on boosting power? 

He also mentioned that he only feels the car shift once. I know it's a 3 speed, but why only one shift (not sure this is related to the lack of power). Starting in 2nd? Not sure that's possible. Any linkages adjustments that might be off? Thanks.