Chainsaw Repair

Hello all, I have a Stihl ms 180 c saw that I have had about a year. Lately I am having problems. I thought it was the chain, but I have a brand new chain and the problem is no better. Here are the details: The saw starts fine, but it boggs badly when I start to cut with it. Every few seconds it bogs to a stop. Sometimes it will not even turn by itself, not cutting anything. The more I loosen the chain, the better it will run, but obviously I can cut like that. I took the bar off and ran the saw and it runs perfectly, nice and powerful and responsive. With the bar on and no chain it revs and runs fine. When the the chain is on it runs a little less powerfully, and when I try to cut it runs pittifully. I have always sued Stihl oil in the gas, and only bar and chain oil for the oil. Like I said, the chain is new and sharp. The bar is original, though it is pretty rough looking. All the paint is gone, and the saw always cuts sideways or off somehow. While cutting I have to constantly pick it up and put it back in to get it to cut. If I take it out of the wood and rev it four or five times it will work up to revving full blast, but once back in the wood it loses power quickly. Also, when cutting, it will die on its own as soon as I stop cutting and let it idle down. It never used to die like that. Without the chain and bar on the saw, it revs, idles fine. The bar doesn't look warped though I suspect it could be without me being able to tell with the naked eye. So, any ideas? This has devloped rather recently, though it has been cutting sideways for a long time. I just thought it was the chain, but it has gotten worse quickly. Should I buy a new bar? Some folks on here have said that they have used the same bar years and years so I don't know if that could be it. Any ideas would be great. I am a novice and don't feel qualified to tear into the carb or anything, though minor things I could handle like checking fuel lines or the plug and stuff. Well, that's about everything I can think of. Thanks for reading.

WAGS

050 chain on a 043 bar,
tune on carb not right Open the L up counter clockwise,
carb diaphragms getting stiff,
 spark screen clogged.  Just a few WAG.

Non adjustable carb. on MS180.  Probably need diaphgram kit.
Shep

Sounds like the bar is bad. remove it from the saw and see if the little sprocket in the nose is moving freely. As far as the saw dieing you are loading it up with to much heat and fuel trying to cut when it won't spin. the carb is probably fine. also has the chain ever come off while cutting? make sure the drive teeth on the chain are smooth on the side as this can cause binding if the chain has come off during cutting and the teeth are rough. Could the angled cutting be caused by the rails gapping on the worn out bar allowing the chain to walk in the cut? Also while the bar is off the saw wiggle the clutch drum(the part that spins freely while the saw is at idle or not running) to see if there is any play + spin it to make sure it is spiinning freely