Not saying that it could not happen, but a company that specializes in rebuilding SU or other carburetors should be able to set them up so that the car will run reasonably well, without tinkering, out of the box. One way to rule out the fuel delivery system upstream from the carburetors would be to hook up a temporary fuel supply - either by using a fuel line and electric pump from a gas can or by using gravity from an elevated fuel supply without a pump. Of course, when working with gasoline, safety is paramount; so make sure to understand how to do this safely. If the car still won't run, and if the spark is strong and at the right time, then there may well be a problem with the carburetors.