Common problem on the 230/250sl series. The factory solved this with the addition of a time switch to momentarily energize the start valve for a second when hot starting. That relieved any hot vapor problem. The 280sl had this newer design.
The easy and preferred method is to install a momentary switch under the dash that activates the start valve at the drivers discreation. Kind of an electric choke. The advantages are you control the starting procedure. It is also nice for the DIYer as you can turn the engine over when working on it [ as in valve adjusting] without gas being pumped into the engine when cranking.
For thoes that prefer to go the stock route, there is a relay and harness kit to modify the system. Email me directly for that info.