My tuned and modded QB79 gave up on me :(

[FRANK]

well my my QB79 quite on me the vavle will not let co2 go out.

I see the firering pin move and hit the vavle but nothing happends I did many test and it seems like its the vavle.

now I need to know how ezzy is it to fix. and I will need a seal kit to do this?

I will fix this QB79 since It was shooting quater size grooping at like 40 yards and I was still setting the scope,
this QB shoots at 766fps on co2 and the grouping was awsome.

I been having lots of trouble with this thing but I dont know why I love it.
probably because I love underdogs that come out winning. but it's losing now.

it's been un reliable. /SAD

[rsterne]

It may be that the filter and/or screen in the valve have disintegrated and plugged the valve.... It may be quite difficult to bleed down the pressure, but critical you do so before disassembly....

Before you take it apart, you will have to make sure it's not under pressure.... then remove the tank.... After you remove the tank block from the end of the tube, you will notice a large slot on the end of the valve.... loosen that one turn and then after removing the valve screws you can slide the valve out the front of the tube....

When you replace the valve, don't tighten the two halves fully, install it, and then tighten the front half to put pressure on the seal....

Bob

[FRANK]

took the tank off but I'm sure there is still co2 in it?
could my vavle be hydro locked? I just had this tuned/modded, and only shout about 300 pellets with it.

ok I will make sure there is no more presur and take the vavle out.

[rsterne]

If you removed the tank (and assuming you don't have a valve between it and the gun) there can't be any CO2 left in the tube, unless the hole in the tank block is plugged and I have no idea how that could happen.... I suppose if both ends of the valve were plugged there could still be CO2 in the valve, but again, very unlikely....

If you find it difficult to remove the screws holding the tank block to the tube then that could be an indication there is pressure trying to push on the tank block.... If they spin out easily, and once they are loose slightly you can move (wiggle) the tank block easily it should be safe to disassemble....

Bob

[rsterne]

Ah well, it was just a thought....

Bob

[AirGunEric]

Check that the adapter the tank attaches to still has the detent pin in place to allow the tank valve to open. If you had no Co2 pressure when disassembling- where did it go if you didn't shoot the pressure out?

[SeanMP]

Check that the adapter the tank attaches to still has the detent pin in place to allow the tank valve to open. If you had no Co2 pressure when disassembling- where did it go if you didn't shoot the pressure out?

I agree by the description the tank valve isn't opening.

[FRANK]

there was pressure, well co2 coming out every time I unscrew the tank.
I will need to take the vavle apart.

[SeanMP]

Have an eye at the sear as well. It needs to be very free. If its not it can slow the hammer down enough to cause a misfire. That particular problem has driven me round the bend a couple of times.

[bitterman]

How did you make out with things? If you are close to Ottawa I could give you a hand with it. I have done some modifications to my sons qb (he is only alow to shoot it if I have 1 hand on it).

The valve looks like someone set it up for either very high c02 usage of HPA. Thats a pretty standard way I have seen alot of them modified.

If you want increased performance but with the stock valve you can most like get alot from a few mods:
-barel port can be enlarged
-Probe the bolt or enlarge the existing bolt for better flow
-Polly seal

The stock valve can be modified for increased flow pretty easliy and still maintain realiability.

If you get a new valve I would remove the filter and screen as they are know to come apart and make the valve fail.

With a dremal you can also port the brass head of the valve for better flow (does nt take much) and since you have a qb79 remove the piecing pin.

I assume you have your PAL as it looks likw you need it with the existing setup.

What is your hammer spring like? It could also be cause your gun not to fire if it has got too weak.

If you are worried about CO2/air usage a HDD would help alot.

Bruce