1966 MGB starts but have to turn it over 100 times first

check all fuel lines for rot and holes , see if there's a squirt of gas when you push the peddle , maybe the fuel bowl is losing it's reserve , carb may need a rebuild

If you don't use the vehicle very often, this is normal. The gasoline in the float bowl evaporates and the engine will not start until the fuel pump, while cranking, fills up the float bowl again. Use a spurt or two of starting fluid or run the engine more often to alleviate the problem. Hope that helps! Jim

Are you using the "choke"? I put choke in quotes because SU carbs don't use a traditional choke but they do have a mixture enrichment device.

Since you have an electric fuel pump, turn the key on and wait for it to prime.