"Light Strike" &/or Blow-Back issue with KJW Para

[scubastevemk1]

I am attempting to repair this gun for a teammate and it is giving me fits.

It is the full metal KJW Para version that is has an almost identical blowback system to the WA Magna found in the Infinity, and others, series. The only difference I have noticed is that the KJW doesn't have the spring loaded rocket valve, rather it has a spring that pushes and one that pulls against the valve between blow-back and firing. I do not have a good understanding of how this is supposed to work and I think it is the reason for my issues.

Basically when I got it it seemed to light strike with propane or 134a. In testing I closed the blowback valve to try to get it to fire, but not blowback. With that done, it shoots as hard as it should. I then blocked off the firing side and found that it still would not blowback.

I have tried changing tension on these 2 springs on the blow-back valve with zero improvement. I have also added and extra half lenght of hammer spring and tried a shortened recoil spring in varying combinations to try to narrow down the problem. I have tried a smaller o-ring inside the blowback chamber. The o-ring that came in it is dark blue and has a fair amount of resistance inside the chamber, the one I have tried has zero resistance inside the chamber. During this time it has alsways "light striked" and shot the bb about 5ft and only partially cocked the hammer upon blow-back, or it has shot hard and not blown back... never with consistent results.

I have since returned the gun to the original order of parts and now it shoots hard, but only blows back hard enough to cock the hammer at the first of 3 stages.

 

I have decided the issue is with the valve inside the blowback chamber, but I do not know what to do from here.

I would like to solve the problem rather than throw parts at it, but if that is the case I may try ordering a factory valve and spring for the WA Magna. I like the idea that a chambered bb holds the valve open for firing rather than a spring pulling against another spring to leave the valve "floating" open for firing.

I am looking for any experiences or input. Please let me know if you need more information to help diagnos the problem. Thanks ahead of time guys!

[Sale]

Check that the valve lock is engaging the valve properly. It could be that the valve shuts too quickly.

 

If the pistol is copied from a WA, the valve lock would be the sliding plate in the top rear of the magazine. When you press the valve, it clicks up and locks the valve open. Pressing the plate down will release the valve again.

 

-Sale

[scubastevemk1]

There is no valve lock on the valve, there is just a solid plate that holds the fork in place to secure the chamber seal. It has the same profile and shape, it even looks like it is a valve lock. My guess is that the valve supposed to function like a valve on a KJW/TM M9 or a Glock variant. WA is the only mag I have ever seen with the valve lock.

Do you know of a way to slow or delay the valve closing to test this to see if it helps?

[renegadecow]

If the pistol is copied from a WA, the valve lock would be the sliding plate in the top rear of the magazine.

-Sale

Copied, but not quite. KJW ditched the system and incorporated the valve lock on the frame and not on the magazine. But that part may also contribute to light strikes. From what I've been through, I've had the following as possible causes of the problem at least on my own P14:

 

cause: valve surface (against valve lock) worn down

effect: valve lock slips and doesn't hold the valve open for prolonged gas release

solution: rotate valve to expose unworn area

 

cause: gummy/worn valve o-ring

effect: valve lock works, but since the o-ring has become more elastic, doesn't make a gap large enough for sufficient gas release.

solution: replace o-rings

 

cause: worn valve lock surface (against valve)

effect: like first one, slips and doesn't lock valve open

solution: replace (as if there are any. its a KJW-only part ) or rebuild damaged area with a sleeve (thin sheet of metal).

 

I've actually had to perform all three fixes on mine along with replacing internal parts for durability, but overall its lasted me for 4 years now.

[scubastevemk1]

I will give those a shot. I had removed that part to see if it made any differance, and it did not. I now understand why. I noticed on both mags I have that the valve is almost polished from contact wear. The lock itself engages the valve more on one side and it has worn there as well. I will try replacing the o-rings and see if there is a way to increase the spring tension on the lock, and modify the face of the lock arm to make full and even contact with the valve. I think rather trying to add material to the outside of the valve, I may try to build up the arm itself, or make one out of steel. Once make of steel instead of crappy cast aluminum, I can carefuly weld up the face and grind it away as needed.

Thanks for the tips, I will let you know how it goes.

 

*UPDATE*

I was able to repair this very quickly, much quicker than I had expected.

The actual repair was done by using solder to build up the worn portion of the valve lock arm, then file down as needed. I used a 60watt soldering iron with a large, round tip to get the valve lock arm hot enough for the solder to bond. I am very sure that this is just a temporary fix since the solder is softer than the aluminum/pot metal it is bonded to, not to mention that it is rubbing against steel while under a load.

I also tried adding spring tension to the valve lock, but the arm on the valve lock was so far worn that it was barely making contact with the valve. This may still work on someone else's gun, or it may work as a quicky repair later when I might not have access to a soldering iron. To add spring tension I removed the valve lock from the frame and found a .112" tall set screw that was the same diameter as the spring to space up the spring and give a bit more tension to the valve lock. As it turns out this was too much tension for my application and it would hold the valve open too long making the gun attempt to full-auto, but basiaclly just bounce off the valve and dump all the gas and bbs. I removed the spacer and it works great.

 

Thank you very much for the spot on diagnosis!

I do not have a copy of the KJW Para manual on the websites that I have. Does anyone know the part number for the valve lock arm so that I can attempt to track down a replacement part?

[renegadecow]

Part #46

You could try contacting them directly at:

kjworks@ms47.hinet.net

[scubastevemk1]

Thank you very much. I will pass the part# on to a local retailer that has always been able to come through with parts when the manufacturer generally ignores individual sales.