Joe, I've never used an 88 or 90 gram cartridge, but I've read that they sometimes send little bits of metal into the valve that causes trouble as you have described. You may need to disassemble the valve to clean it out. You may also need new seals from Crosman.Then you can just buy an adapter to use 12 gram cartridges. Amazon search this:"12 gram to 88 gram co2 adapter"You will find several like this:https://www.amazon.com/sspa/click?ie=UTF8&spc=MTo1NTI3ODAxODQ4OTIyNDA0OjE2NjI3NDAzNDY6c3BfcGhvbmVfc2VhcmNoX2F0ZjoyMDAwNjM2Njc3MDY5NzE6OjA6Og&sp_csd=d2lkZ2V0TmFtZT1zcF9waG9uZV9zZWFyY2hfYXRm&url=%2FCPROSP-Adapter-Anti-air-Leakage-Gaskets%2Fdp%2FB08R8K1L3N%2Fref%3Dmp_s_a_1_2_sspa%3Fcrid%3D1MIYFY65YBD4U%26keywords%3D12%2Bgram%2Bto%2B88%2Bgram%2Bco2%2Badapter%26qid%3D1662740346%26sprefix%3Dco2%2B88%2Bgram%2Bto%2B12%252Caps%252C166%26sr%3D8-2-spons%26psc%3D1Hunter
I have located a complete main tube. I think it will be just a remove and replace sort of action. I'll stand by for a day or so before I order it. I want to go to the 12 gram. I do not shoot enough to warrant 88 grams of CO2. It might take me a year to utilize that much air.Joe
Thank you for your comments. Much appreciated.I've been going back and forth examining the AS2250XT. What I thought was just a safety strut is a gas transfer tube from the 88 gram connector to the normal 12 gram cartridge main tube. That way the trigger and striker would work normally without modifications. I removed the threaded plug on the front of the main tube and looked inside. I could see where the gas transfer tube port enters into the chamber. Then I had a "Ah Ha" moment. I noticed there was no o-ring on the threads of the plug like there is on the same plug on my Crosman 150 (which holds pressure for months). I am certain I have never removed that plug before. It is possible it was omitted during manufacturing. I think that might be the simple problem all along. The gas from 88 would just leak past the threads of plug. I'll take the plug down to the hardware store and find an o-ring and give it a try. It will only cost me the price of an o-ring and $10 +/- for 88 gram cartridge. I can see where there could be problems all along the connections of the gas transfer tube if it was not just right.I'll report back.Joe
Finally, I have assembled all the parts to make the transition. I have learned a lot on the 22XX family. I do not know if I have an issue with the safety. I did not remove the trigger plate off of the grip frame so the safety should be intact. What concerns me is it moves effortless back and forth through the grip frame. Seems like I should feel the resistance of the spring. I cannot see how the spring and ball could get out. I'll know for sure when I get it all back together.Joe