I have a miller mig welder. While welding for an hour or so, I started to get porosity in my welds. This is normally caused by lack or problem with the shielding gas. I have tried everything. New gas bottle, regulator, tip, tip adaptor, O-rings in gun, & wire. I check all lines for leaks, verified selenoid is working properly and checked over gun lead and liner ( which was removed and cleaned ). I am stumped. When I crank up the gas at the regulator I improve the weld but still not right. The only thing I can come up with is that the gun lead must have a problem I can not see or find. Their is nothing left to check as far as I know. If anyone has any ideas that might help, I would be forever in your dept.