Valve issue

[angrybear]

I have much confusion-ness & seek the advice of the all knowing collective 

After playing with my .25 FAC I realised the power was not as it should be, it had been doing 44/45ftlbs with the original valve (bronze filter type)

after a play at regging it, (that failed) I went back to the FF but was only getting 36ftlb, I then remembered a post about valve size, had a measure & sure enough new valve was only a 4.7mm bore, the original is 5.6 ish so right thinks me, I'll ream a spare one out to 6mm & that should give me a bit more oomph

Just tried it & power dropped from 36ftlb to 28ftlb no change other than the 6mm valve which has me very confused.
Any ideas other than the obvious of go back to the filtered valve.

[Daztilley]

If you change from a filtered valve to a standard valve be aware that the valve cap in the block is different for the 2 types. It can help to have a delrin insert made to sort out the issue. @KevG made 1 for me in the past 👍

[Squinty]

Could be that 6mm is just that tad too wide for fastflow?
Found with my FAC  .22 that leaving the regged valve in with take 40% off the output even if it is consistent

Maybe check the top port sizing of the filer valve and your spare?

[Brooksy]

Having gotten rid of the filter, did you make a spacer for the valve spring?

[Squinty]

could be the longer stem spring that you have used, I bought some a while back and they sapped the power

[angrybear]

When the filter valve set up was initially removed, I got a new 'FAC' valve, end cap with an insert & longer spring from Dr Bob, which I used for several years, before trying to reg the rifle, but I'm not sure which of my valves that one was as they're all in the same bag (apart from the complete filter set up).

As it happens taking it apart again, this morning might have solved the problem, there's damage next to the side pin recess so the 6mm valve might not have been pushed all the way in    meaning the top port not aligned correctly  so it might well be finger trouble from muggins here.

I'll try it again this afternoon now I'm calm again.

[KevG]

found 5.5mm front port best size for fac fast flow.you have to be careful with length to stem to,standard is best.41mm from were the stem spring sits to back of valve stem tail.also best with return spring between 19 to 21mm.to long a spring and to much stem length can get you coil bound plus loose power and risk of damage.
kevG

[angrybear]

Thanks Kev,
I've gone back to basics, removed the QF, refitted the filter valve & what I'm pretty sure was the hammer spring fitted when I bought it,
which has got it back to 811fps 37.1ftlb, (JSB 25.4gn) but it's still down a bit, on what it was.
I'll check the stem length because I've got several stems & can't remember which was the original, maybe the one with a single groove ?

I did retry the 6mm valve, making sure it was fully home sure enough only 711fps 28ftlbs,
but I have to say mega consistent shot 2 mags for a 4fps spread 

[angrybear]

As if there had ever been any doubt in Kev's genius 
sorted my parts to find the closest fit to his above spec,
My valve is a smidge under at 5.4 & the exhaust spring a tad short at 17mm but now back to 865fps for 42.2ftlb.

As a point of interest I refitted the QF & it dropped to 834fps - 39.03ftlb, removed again, back up to 865fps,
I suppose it should hardly be a shock when you realise the QF has a single hole <2mm, so next idea will be to put a couple more holes through to increase the flow.

[KevG]

nice one,yes the quick fill will choke it down with a single 2mm hole.
kevG