The MCP outlet (stinger) is 9/32" which is a little bigger than most use on their cans. I'm pretty sure the problem is excessive pressure in the fuel tank and I even thought about putting a pressure relief valve in the form of a one way valve tee'd off the tank vent with a fine tuned spring in the valve.

The only other thing I can think of as the cause for this spitting would be that the can is somehow sending a "Bad" wave back up through the enigne's intake system. This could be maybe remedied by tuning the can differently as suggested by Jim (thanks, Jim).

Big Mike