450slc with no power

My 450slc just had the fuel relay, fuel filter, and water pump replaced. I took it for a ride after this was all done to check for leaks. We drove it around for about an hour withno problem. While we were out i put some premium fuel in the tank. The next day i discovered a small amount of water on the floor and discovered i missed tightening a hose clamp. I tightened it and then started the vehicle. At that point when ever i tried to give it a little gas it would hesitate,back fire, spit & sputter like crazy. After it warms up a little i can get it out on the road but it takes about a mile to get it to about 50mph. I checked to make sure there wasn't water in the fuel and it looks o.k.. Does anyone have any idea what might cause this missing and lack of power problem?

if not an air or vac hose loose,i would suspect the engine coolant temp sensor.

I had a 450 slc that I had to change the water pump on...you have to remove the distributer to get the water pump out...check to see if it got put back in right and the timing is correct.