QB79 mod Delimma

[Bentong]

I did  power mod on my qb79 and got her to shoot 648fps with 14.3 CPHP. My mod  for the valve consisted of removing the piercing pin, felt filter, poly  tube port, open up the bolt probe to match the bottom opening on the  port & front that pushes the pellet in to get to 650fps with no  problem. My goal was to get to at least 700fps so I tore it back up and  drilled the valve hole bigger, notched the washer holding the valve  spring and trimmed the valve stem face but made sure the spring still  hold it in place. While doing this I nicked the valve O-ring and had to  use my spare one from my QB78 cap for it's bulked filled right now. When  I got everything back and charged it but it won't fire (indoors 73'f). I  used the same spring on the valve and hammer. So my question is, when I  opened up the valve for more CO2..did it cause a valve lock? Can I just  replace the valve spring to a weaker one or shim the hammer spring or  combination of both. Right now I don't want to open her back up until I  get the O-rings I ordered.

[fisherdude]

Since no one else has answered, I'll take a shot at this.  Could be a couple of things:

1. The hammer/spring group may be incorrectly assembled.

2.  Valve may be incorrectly assembled.


When you get it figured out, post the solution so all of can see how you fixed it.

[Bentong]

I got it sorted out yesterday. She's now shooting but still short of my goal of around 700fps with 14.3CPHP with 72 temp. I know she's shoot harder when it hits 90's here. I have to borrow the front half valve on my QB78deluxe.  I slap it on and fired. From what I have, I started replacing the 79 parts back in starting with the open up tube, washer, spring and it's still firing. So the culprit was the stem valve seal. I reshaped it and must have taken too much. I'll place my modding on hold until I get my delrin stem seals on hand to get 700 fps and get the QB78 up and ready for summer.