Poulan Pro chainsaw,46cc,the chain adjuster keeps loosening up while running, need a new adjuster/tightener?

First, I'd read the manual if in doubt. No matter the type of adjuster, tool-less or not, you loosen the bar nuts, tighten the adjuster until the chain just touches the bar on the bottom (while holding the bar nose up) then tighten the bar nuts. Chain should move easily.
Re Poulan chain tightening. Be sure it's oiled and sharp, of course.

CHAIN STRETCHS AS IT HEATS - KEEP CHAIN TIGHTENED CORRECTLY AND ALWAYS KEEP OIL IN OILER AND MAKE SURE IT OILS THE CHAIN. IF THIS DOESN'T FIX - REPLACE THE CHAIN. IF IT STILL HAPPENS THEN REPLACE BAR. WILL FAIL AGAIN WITHOUT OIL. POULAN WILL NOT HOLD UP WITHOUT CHAIN LUBRICATION. WORSE THAN OTHERS. IF CHAIN OR BAR OVERHEATED YOU'LL WORK ON IT MORE THAN YOU CUT. OIL IS THE KEY TO CUT WITH A POULAN!

First, RTFM- read the manual. Lost it? No problem, download it from Poulan PRO website page for PP4620avx. Pick a version you like, save and read it. Google is your friend.
Chain Adjustment Part cut and pasted as follows:
Adjusting the tension:
Chain tension is very important. Chain stretches during use. This is especially true during the first few times you use your saw. Always check chain tension each time you use and refuel your saw.
1. Lift lever on bar knob and turn counter-clockwise 1.5-2 turns to loosen clutch cover.
2. Turn adjusting wheel (downward direction) to tension chain until chain solidly contacts bottom of guide bar rail. Lift tip of guide bar while adjusting tension. Tighten chain Adjusting Wheel
3. Use a screwdriver to move chain around guide bar to ensure all links are in bar groove.
4. While lifting tip of guide bar, tighten bar knob securely (clockwise).
Hand tighten only.

Be careful not to destroy the adjustment mechanism. When it breaks, go for a clutch cover with the simple adjuster that needs a "scrench". Longer term, learn how to search this info. Saves time. Now you can work on sharpening chains- very important.

Manual page:
http://www.poulanpro.com/ddoc/PPOO/PPOO2006_USen/PPOO2006_USen_PP4620AVX_952802146.pdf

Before putting your hands near saw chain cutters, put leather gloves on. Cutters sitting still can still draw some blood.
Loosen the nuts holding the clutch cover, loosen the adjuster, then remove the nuts. Remove the cover. Slide the bar along the studs, free of the adjuster, toward the clutch. Revove the chain from the bar groove, then move it clear of the clutch drive. It's now off. Good time to clean bar grooves and bar-mounting area of dirt & chips.
Reverse the procedure to install a chain, making sure the cutters have their cutting edge facing forward on the top of the bar. Make sure the adjuster is engaged with the bar before tightening the nuts at all.
Holding the bar nose up, tighten the adjuster until the chain touches the bar on the lower side. Tighten nuts.
After short run to clear any debris, recheck the chain tension.

If this is the tooless adjustment, it sounds like the small gears in the cover have stripped, remove the side cover, turn it over and remove the cover over the tentioning mechanism, replace parts as required.

are you talking about the magneto to the flywheel gap i just use a piece of paper between the two and tighten it

If you've got the adjustment all the way out, you may need to remove a link or two from your chain or replace the chain. You can find replacement chains at Partsbuggy.com.

the adjustment screw near the end of the bar( next to the engine) needs to be turned in to tighten the chain just don't tighten it to much

Is it fitted with a tool less adjustment device? See Operator's Manual. Normal configuration as below:

Chain adjustment

1. Make sure the chain brake is off (gloves will protest your fingers).
2. If necessary, loosen the bar nuts that are clamping the clutch cover in place (or whatever holds the clutch cover and bar on). They don't need these really loose - finger tight will do.
3. Ease the tension adjustment until the chain is obviously loose.
4. Using one hand, hold the nose of the bar up.
5. While holding the nose up, adjust the tensioner so that the center of the chain just touches the underside of the bar, add a touch more.
6. Continue holding the nose of the bar up & tighten up the bar nuts / bolts / quick-release system. HTH

Lou