Marauder 25 FPS

I'd be happy with 760 fps if the deviation was small and I got 3 mags on a fill. Having said that, Make sure your VMS (valve metering screw) is backed out 5 turns from all the way in. You can increase hammer spring tension and lengthen the hammer throw to get more power. Maybe AJshoots will chime in, he really knows the Marauders.

Unfortunately AJ doesn't come over here as much anymore. I for one really miss his posts , always informative and to the point. Didn't even know me and offered to get me out of a mess. BUT, I'd bet if you sent him a PM he would give you a reply.

I have a WARized .25 caliber Marauder, with a TSS, bottle, and regulator set at 2,100 psi. I shoot the AirArms 25.4 (same as JWS 25.39) at ± 867 FPS. Accuracy is very good at under 3/4 inches at 50 yards if I do my part. 

The 33.95 JWS heavies barely hit 750 FPS, and the accuracy isn't very good past 30 yards. 

But to echo John, if it is shooting well, don't mess with it. 

A lot of the numbers your going to see on the net aren't from stock guns. But if your needing more power and are comfortable with trying to tune your gun do want JohnL57 said. Just know this can take some time and pellets. I didn't do much tuning on my .25 before putting custom parts in, but it did get really close to 40 fpe. Getting a tss from wicked air would be my first recommendation. You'll still get about 40fpe and a lot more shots then just using the stock spring. Easy to install and tune.

What are you planning to do with your gun? If you are plinking in the back yard, the lower fps will give you more shots per fill. If you will be hunting, the higher fps makes it easier to calculate hold over values.

I fully get not wanting to mess with a gun that is shooting good. But if its not where you want it your going to end up not shooting it. And you can always tune it back to where it was.
Alan, i'm guessing the 33.95 pellets are going to slow and are destabilizing.