Hi Sir or Madam, I look forward to resolving your electrical problems.
Please provide more information about your project. A NEMA 6-50R is a straight blade receptacle and a NEMA L14-30P is a locking plug. The two cannot mate, it is impossible. It is also highly inadvisable and unsafe to mix amperages of devices in a device. The amperages of each device should match the rated output of the device.
You need to get the matching L 14 30 P (male plug ). Connect the grounnd green , off the 6-50 P you strip and cut off, wire to the green screw of the male plug (L-14-30 P). The silver screw does not connect to anything because your 6 - 50 P is just 2 hots and a green ground. All that is left is the 2 hots from the 6-50 P, these terminate to the brass colored screws of the male L -14-30. Make sure no stripped cable or copper is hanging out of the backside of the plug when you put it together. Read the directions to make sure your plug is put together properly and it is not loose in any fashion. Finally make sure the voltage rating of the equipment you are hooking up matches the voltage rating of the generator output Recept. O.K current you said is not the issue but voltage will be if you don't make sure.