6 replies to this topic

[MattPaintballer]

I got a NIB SM750, old school version. I have yet to modify it or even open it up. Ever since I took it out of the box, it's had this weird pumping problem. I have to pump slowly and steadily, and make sure I pull the pump all the way out, then push it all the way in. Otherwise there will be no resistance in the pump and it will not get air. Sometimes, even when I'm careful, it still gets no resistance. Sometimes when it gets no resistance, I pull it back as normal, then when I push it in, it seems fine. But when I get to the pump cap, the pump snaps back. Sometimes I hear a pop, sometimes not. Sometimes there is air in the tank, sometimes not.

There has to be something wrong, because I talked to PCMadness and CT, and they both said their SM750s don't have this problem. It is quite the annoyance and I want to fix it, but I don't know how.

[The Infinite Shindig]

I would in no way call myself an expert on most gun internals, but I have a feeling it could be a problem with the O-ring that is at the end of most pumps. The reason for this is that it sounds like the pump does not have a proper seal with the pump shaft. My suggestion would be to head to the hardware store and buy a few O-rings for less than 50 cents a piece. You usually can get O-rings in a variety pack, but you might be better off taking the old one with you in order to get a decent sized fit.

[ompa]

It also may be the check valve, located at the end of the pump tube. Unfortunately, if it's that, it's going to be a bitch to fix. I'd suggest just replacing the pump tube with a different pump tube if that's what it is. Although, it's going to be even harder to attach a new pump to the chamber, looking at the internals.

~ompa

[MattPaintballer]

So basically I'm screwed?

[ompa]

Not if Shindig's right, I'm just saying if he isn't right, chances are, that's the problem. Although I'd suggest trying to plug the pump as well, it may possibly be that (aka plug the overpressure release valve). If you plug the valve, replace/fix the o-ring, and you still have the same problem, then chances are you're in the situation described in my last post, and you are indeed screwed.

~ompa

[One Man Clan]

I'm pretty sure TIS hit the nail on the head. I have the same problem with my Big Salvo. The problem comes from the fact that there is a slight variance in what the bubber does over time. You can even find new o-rings at the dollar store, look in their shitty tool section.

[Ash]

Those are the best suggestions... however, I just want to warn you that the old SM750s are extreemily problematic. They have many problems with the pump and the valve mechanisms and such. We must've gone through about 8 of them back when we used to actually use them.