Guys I need some help...
I helped a buddy out and replaced a paint set on his EFI 2010 Harley Fat Boy. I am not sure of the year bike the new tank and fenders came off of but they bolted up with no problems. The fuel sending unit and pump fit in the new tank the same way it came out of the old tank.

The difference is his old tank had a vent (nipple) on the very front of the tank that connected to the vent bypass hose that goes down and under the tank along the frame rail, the new one does not...

The tank is building a great deal of pressure with the cap on tight and it coughs and sputters when it runs
But without the gas cap on the bike won't run!

Who knows if that vent tube has some connection to the EFI or could this just be a purely venting issue?

Any help ideas or suggestions are welcomed!

Thanks,