One thing to look for is a seized gas adjuster..very common to find, another is a corroded gas piston and cup, you think a Yugo with a leaky gas valve is a pain in the arse... if this part is leaking, adjustment is futile, your pissing away your life, alot of time and ammo. Now, replacements are available..
http://www.ppsh41.com/SVTitems.html This is what is in mine...courtesy of a lack of cleaning and attention in the past to the gas system. Also, a gas adjuster wrench will come in handy...I plucked one off the Fleabay.
When you go to adjust, start on the lowest setting, 1.1..the scribe lines must line up on each setting, what your after is the minimum amount of gas to cycle without issues, you want absolute consistency on ejection, that is it's happy place. You do "NOT" want to over gas it and make it sling empties in to the next county, all your doing is beating the rifle to death at that point and might even destroy things like the extractor, recoil springs, and back of the action. Mine will drop the empties about 5-7ft away, I've seen some chuck them 10+ ft, thats a bit much. Mine is happy with Czech ammo on the 1.3 setting If you change ammo, brands, countries of mfg, bullet weights, anything, start over and readjust it, it's yours, do what you want, but your better safe than sorry in the end.
Another thing, if you have dummy test rounds, make sure it feeds from the mag, it's not designed to do mag swaps like an Ak, it was primarily designed to be loaded with strippers. If someone ever dropped the mag on the feed lips and bent them, you will have some fun readjusting them. This is why they are serial marked, each was adjusted to the specific rifle, it may or may not work in another.
It's a cool rifle with a great history...but I would be damned if I'd carry the thing in a war, heck, I don't care much to shoot it, much less clean it.. it is a bastard to clean compared to most weapons, finicky, heavy and lots of little parts and crap to go wrong. Actually I find most of my Mosins are more accurate than the SVT, but that could be anything causing that. But, hey it sure looks cool... Mine is actually one like P32 was talking about, the Finnish capture and the Finns refurbed it.
Cleaning rods are ungodly expensive and beware of crappy bores, ones with purple bolts are usually Russian refurbs, Finnish are usually in the natural white and stamped [SA]...that about sums it up