5th Gen VFR Fuel pressure regulator wont open

I have a 2001 VFR800 that I bought just this last week, it had been sitting for over 3 years in the last owners garage and because of this the fuel pump went out, and a bunch of gunk formed in the gas tank. I was able to get the pump going again and the tank cleaned but now the fuel pressure regulator wont open to return fuel to the tank, this leads to it running too rich and stumbling hard with throttle. I have replaced it but no change, and I have verified that there is no gas in the vacuum line connected to it. Any help is appreciated, Thanks Jackson

 

Are you sure the pump is delivering enough pressure to open the pressure regulator.
You could hook an air line up instead of the fuel line and carefully increase the air pressure. This would confirm if it is truely not opening at the proper pressure. Then you could go a little bit higher and see if it will open.

Did you clean, back flush or replace the fuel filter? Could it be causing a large pressure drop?

I'm wondering if your revived pump is still weak and the stumbling is actually fuel starvation vs too rich?

Good luck.