Cold start problems

My roommate has a 1973 450 SL with 98,000 miles. I'm thinging about purchacing.
It was not well maintained.It does have a new dist. cap, points, condensor wires and plugs. I replaced the fuel pump and all flex fuel lines from front to back (dry rotted and leaking). When the car is first started and driven it bucks like a bucking bronc. When it warms up the bucking stops but still lacks power (0 to 60 in 20 sec). On one ocasion when I started out cold from a dead stop the engine reeved to 3000 rpm and didn't move for a few seconds. It never happened again when it warmed up. Any sugestions would be helpful.