Zap ZXS 800e Mods
It's an interesting design, not without both fault and bonus. The solenoid valve is actually a 3-way, same as used in tandem on the old NitroDuck E-cocker. It's coupled with a pneumatic boost valve, basically a bulky way to make a piddly little valve flow like a big'un. Unfortunately this is why it takes so much grip to house it. For it's bulk, ZAP (or whomever designed it) did a good job of keeping everything inside.
In this design, the ram is the bolt, but not in the cool Sovereign way. It's actually a pretty cool idea. The bolt's tail acts as the piston in a spring return ram. Regulated gas is fed to the tail of the bolt driving it forward (compressing an internal spring), closing the breech and hitting the pivoting valve toggle firing the ball. The "control pressure" is cut off and the spring internal to the ram forces it back to the open position. Cool! So simple!
A note on the valve. It is indeed a standard pin and cup valve turned on end. The only other mass produced gun with that valve style was the 'Cat series from ICD. Unfortunately Zap went a different direction. Instead of designing the bolt to open the valve in a similar direct method, Zap's designer added a toggling "link" above the valve pin, that's hit by the bolt. This causes it to pivot down into the pin, thus opening the valve.
This is all well and good....or would be if the manufacturing were any good at all. The edges of the link is really rough and a poor stamping such that when coupled with the side to side wobble that the link can do means that the consistency is rotten. I too saw +/-45 fps.
Mine now shoots +/-4 on compressed air and is actually pretty fun to shoot. Here's what I did:
1) NEW LPR!!!!! The stock LPR is marginal at best with swings from 35 to 130psi on a 100psi initial set! I milled a new air block from aluminum and ran a generic drop forward to a female Stabilizer and a T- fitting. I ran the LPR on the T next to the Stab and a hose up to the gun on other side. This cut the fps swing down to +/-20fps. Not a bad start.
2) Next I concentrated on the valve setup. Filing the faces of the link nice and flat and shimming up the side slop really nailed the velocity fluctuation. Got it down to +/-6fps, now we're getting somewhere!
3) The bolt is horrendous! It's the worst piece of cast crap I've ever seen. Neat idea but bound by the worst of manufacturing. It's edges are rough, the surface is plated...sorta but it's rough to the touch too. All this and it's a leaker too. The amount of blowby up the feed's pretty amazing too. No need for an agitated loader, the feed'll popcorn too much to jam.
I turned one out of aluminum and skinned it with delrin that was then turned to fit the bore of the bolt tube as closely and smoothly as possible. Now there's almost no perceptible blowby and the gun went up from 285 to 340fps at the same reg setting. Cool!
Lastly, the valve chamber casting flow issues. The hole thru the bottom of the body into the bolt is pretty large and oval in shape. The transfer port from the valve up to the bolt is small in diameter and poorly cast. I drilled it out to 11/32", matching the body and bolts ports. The velocity at the current setting is 365fps.
Adjusting the velocity via the Stabilizer is great and it now shoots between 295 and 301fps pretty consistently. A couple set screws in the trigger and it now rocks like mad. I'll enjoy taking it on the field now and then to eliminate a few IR3s.
I'll be giving it a conditional thumbs up. It's a great project gun if you're capable of some pretty heavy tinkering.