Any S400 gurus out there?

[Simonsays]

Just acquired my first pcp, an S400 carbine (thanks Dave :-))

I notice that the sweet spot occurs at the relatively low pressure - around 135-100 bar. This doesn't bother me per se but over 150 bar the power is below 9ftlbs (rises to around 11ftlbs at 125 bar or so). So I cannot escape the feeling that I am not getting everything from the gun in terms of spread and shot count.

I got an improvement after cleaning the hammer rail to get to this point. Prior to this it was around 7ftlbs at 150 bar which clearly ain't right.

Could it be the hammer spring being weak and not overcoming the pressure of the exhaust valve? Any pointers where to go please?

Another thought was that the pressure gauge reads low - but it agrees exactly with the pump so they would have to both be reading low the same amount which seems a little unlikely.

[Stu83]

If the hammer spring is worn, you could be right in thinking there isn't enough tension to open the valve. Im guessing its an older s400?

[larrylamppost]

either the hammer spring is too weak or the exhaust valve return spring has too much preload because the pot has been wound in too far,i'd go for the pot being set wrong myself.

[Gwylan]

As Larry says, someone's had a real mess around, probably with the firing pot, it should be set at a certain length of thread, which I've forgotten.! also check that the TP O ring seal, (easily lost when stripping,) and breech seal are in place. The sweet spot on a Classic at 11.3 fpe should be around 50 shots from 170 bar to about 100 bar. I'd be surprised if its the hammer spring, cleaning and polishing the hammer rod makes the rifle more consistent, if it's really gunked up it might drop the power, but not by that much.

Gus

[larrylamppost]

58mm of pot showing is what i always set them at.

[wezdavo]

As Larry says, someone's had a real mess around, probably with the firing pot, it should be set at a certain length of thread, which I've forgotten.! also check that the TP O ring seal, (easily lost when stripping,) and breech seal are in place. The sweet spot on a Classic at 11.3 fpe should be around 50 shots from 170 bar to about 100 bar. I'd be surprised if its the hammer spring, cleaning and polishing the hammer rod makes the rifle more consistent, if it's really gunked up it might drop the power, but not by that much.

Gus

57mm Gus

[larrylamppost]

57 with a new hammer spring,58 with an old one.

[Simonsays]

If the hammer spring is worn, you could be right in thinking there isn't enough tension to open the valve. Im guessing its an older s400?

Yes its an older pre AT. Easy to pull apart.

Thanks all for your suggestions. Looks like firing pot, valve spring and maybe hammer spring. Its got what I assume is a preload washer. Does it make sense to add more preload?

[Gwylan]

Thanks guys, I must write that down.!

Gus

[u.k.neil]

Get a new hammer spring from Julian Bond and set the pot to 57 mm mate.

Neil

[Kingplinker]

Hammer spring as I said Thursday then use the Ventura screw to fine tune it , failing that get a springer .lol

Julian Bond offers a great service for parts , turnaround is quick too .

Atvb

Dave

[max headroom]

Hammer spring as I said Thursday then use the Ventura screw to fine tune it , failing that get a springer .lol

Julian Bond offers a great service for parts , turnaround is quick too .

Atvb

Dave

not a lot of people know where the venturi screw is. good job. dont want every bggr fettling,

[chris.e]

Similar thing occurred with mine a few weeks ago and all it needed was a good clean.
Strip it down, check that the nylon valve head isn't worn, set the pot to 57mm and give everything a good clean.
You could change all the seals while your at it if you think it needs it.
If it's still not right and assuming the valve head is ok then look at replacing the valve and hammer springs.

[Kingplinker]

not a lot of people know where the venturi screw is. good job. dont want every bggr fettling,

Quite , apologies also as spell checker obviously thought I was writing about an ace pet detective .

[Simonsays]

Similar thing occurred with mine a few weeks ago and all it needed was a good clean.
Strip it down, check that the nylon valve head isn't worn, set the pot to 57mm and give everything a good clean.
You could change all the seals while your at it if you think it needs it.
If it's still not right and assuming the valve head is ok then look at replacing the valve and hammer springs.

Thanks very much one and all. I'll get onto it....