I have a similar situation with a Cap 232 and my solution was to fill through a third line. I put a T connection in the vent line which is normally plugged. I also made the vent line to the muffler long enough that a small loop emerges at the bottom of the cowl. I use a clothespin with a rubber band around the end to pinch that portion of the line when fueling, and the other end of the vent goes back to the fuel jug. The clothespin prevents fuel from going through the vent into the muffler. Just remember to remove the clothespin.

Note that I originally tried to use a Hemostat, but the hemostat had a tendency to cut the fuel line. The clothespin works better and cheaper.

Brad