The only way too keep two edges parallel too each in most of our shops is with a table saw or a planer. Without seeing your jointer, it sounds like there may be a couple things going wrong......1. Make sure the outfeed table is dead even with the tips of the blades. An easy way too do this is use a framing square or a good straight edge and lay it on the outfeed table.....roll the blades of the jointer until you can just barely feel the tips scraping the straight edge. This is also an easy way too make sure all the blades are set at the proper height if you dont have magnetic sets. 2. Make sure you only take one or two very thin cuts with the jointer......every time you run the board across the jointer, you risk runout.
Another thing too check is the table saw. Using your miter gauge, set the head at 0* as if you were going too make a 90* cut on the end of a board....push it down so the front edge is even with the front of your blade. Clamp a framing square or thin straight edge too the head so the end of the square is just a hair off the very edge of a tooth....note the tip of the tooth and make sure it is a tip running toward the side of the square. Now then, push the miter gauge down the slot too the back of the blade and make sure the tip of the tooth at the back of the saw is the same distance from the tip of the square. You will need your blade all the way up for this procedure. Another thing too check is roll your blade and make sure your blade is not warped by watching the gap at the end of the square.....it should stay consistant!. All blades will have a little runout but it should be very very little!!!.
If the outfeed on the jointer is right and the blade of the saw is running true too the table.....then next we check the rip fence too make sure it is running true too the table. Slide it over too the edge of the T-slot in the table. Or the edge of either slot and tighten the fence....notice if the fence is exactly parralel with the slot in the table. If not, we have found a major problem!. There will be a way of fixing this but all saws are different and you may need too refer too the owners manual for proper method of adjustment. Just about all manuals are available on line, just type in the model number and name of the saw in the search bar and surf through the available sights....most of the time, you can find a download for the manuals.
Table saws are finicky creatures and it takes a lot of patience and time too perfect the adjustments on them....but its time well spent as a properly adjusted saw is less noisy, makes beautifully straight cuts, and is a dream too work with.
A few of the things I look for if a saw is out of adjustment are:
Noisy running, excessive whine.
Having too push and force a board through the saw.
Smoke!!!!!!!! Even a bad blade with little set will still cut if the saw is adjusted properly.
Hint: Most of us cannot do it because of space, but a properly floor mounted saw is far more accurate than one sitting in a roll around base or even just sitting on the floor. Concrete anchors with double nuts for leveling, or bolts in a wood floor with proper shimming or jam nuts are far superior too keeping the overall plane of your saw accurate!. On this same note, it is important too set level too the top of your table and not the bottom of the legs on your saw. Always use a good level on all four sides when setting a tool and bolting too floor, or do like I do and set up the transit and get it right!. Another key feature of bolting down your tools too the floor is stability, your tool will run smooth and quiet!. The vibrations associated with lightweight table saws will become almost nonexistent!.
I hope yall dont think I'm rambling but I'm merely trying too cover all the bases that I know of!.....Hope this helps. I'm sure there are lots of other ways of doing this but this is just how I usually do it and it seems too work!..... Best of luck and let us know what ya find!.