I use a length of brass tubing with a short piece of the next larger size soldered to the end, tube should extend to about the middle of the widest part of the pipe. For 3.5cc I use 11/32" (0.312" I/D), 7.5's 13/32" (0.375" I/D), 11cc and up including 27cc gas motors 15/32" (0.437" I/D). You may need to stretch the stinger slightly, on aluminum pipes you can heat it with a torch and use increasingly bigger drill bits to work it out, or if there's enough material you can just drill it out. You can use the next smaller size tube but watch for excess motor heat in hot conditions.
