leaking regulator

[NeilMac]

Not having taken a note of the reg pressure before you started, you are kinda in the dark, but if at 100 bar the rifle is not performing, then you need to go lower. Steyr regs run at 85 bar so do Walther regs, Anschutz can be lower than that.

You have done nothing but alter the reg pressure, so nothing else in the rifle should need changing in order to get to more acceptable velocities.

[Shed tuner]

You have done nothing but alter the reg pressure, so nothing else in the rifle should need changing in order to get to more acceptable velocities.

had the rifle been chrono'd shortly beforehand, this woudl make perfect sense, but it could have been doing 7 Fp beforehand - most likely is crap / sticky hammer I'd guess, unless the spring itself has failed. 85 or 100 BAR won't make a huge difference to power if the rest of the rifle is correctly setup

[dayglowfroggy]

I Would change things very gradually since you haven't touched them just the reg .
The o ring that is inside if it's like a tench reg just needs winkling out with a not very sharp poky thing.

On a bsa you just turn the power adjuster screw to set the power not sure what s400 has.

[NeilMac]

had the rifle been chrono'd shortly beforehand, this woudl make perfect sense, but it could have been doing 7 Fp beforehand - most likely is crap / sticky hammer I'd guess, unless the spring itself has failed. 85 or 100 BAR won't make a huge difference to power if the rest of the rifle is correctly setup

You are probably right about the reg pressure, 1200 psi vs 1450 psi and yes, had the gun been chrono'd then there would be a baseline.

This is not helpful to the OP who is just trying to get his gun working, but I'm afraid this is typical of what happens when people go inside rifles. I have seen some terrible messes inside rifles that 'nobody touched'. I know we have all learned through experiment and the best guns to experiment on are your own, but pcp's and regs can be mighty frustrating, even when you know exactly what you are doing.

To the OP. The 400 has the firing valve and its return spring in a little brass 'pot' / closed tube. You need to mark it and the action with a pencil or sharpie line, then after you have found and undone the locking grub screw (3mm I think) you can unscrew the pot and get to the bits inside. The firing valve may need a clean and the face a polish. It also might be that the valve is actually sticking. Sort that out and put it back together making sure the pot is returned to exactly the same point it was before.

The it will be back to the reg.

Have a search on youtube, there may be a strip down tutorials there.