I purchased a used 440.  The saw looks near new and I took the muffler off to inspect and the piston looks near perfect.  I ran compression test and it is getting 125 psi of compression.  It will start, but not stay running.  It seems to make a hammering noise when running.  I cleaned the carb which seemed to be in great shape, and got not change.  I ordered a replacement carb on amazon and it still seems to run the same.  I have taken the carb off and on numerous times and can not see any reason why this saw runs badly?  I tried doing some adjustments to the carb low and the idle screws, but not making much difference.  I am pretty new to repairing chainsaws, so any help would be appreciated.  I have a short video I can share but the forum does not seem to allow for videos.
Thanks in advance for any help
 
 

Can you post a video on You Tube?
 
Also, the "hammering makes me concerned.  Get to both the clutch and flywheel sides of the engine and check for any up and down play in the crankshaft.  
 
Play in there will cause a vacuum leak in the lower end causing running issues, especially lean running issues. 
 
 

I did like you said and uploaded the video to youtube.  Here is the link.  I will look for play in the crank shaft after work today

 

 
 

It will not let me share the youtube video link
 
 

https:// youtu.be/4gWZbwWRps8 you will have to remove the space in front of the slashes
 

No links showing.  You may have to slightly separate the link so it'll post. 
I can copy/paste and put em together..
 
New members have some restrictions on them.. :(
 
 
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I gather the clutch brake was NOT on on that video?
 
There seemed to be much drag on that chain/clutch.
That chain seems WAY TOO TIGHT...
Make sure that chain/clutch spin freely with the brake off..
 
That noise shouldn't be there, and doesn't sound good however, peek at the clutch, there may be something amiss in there knocking about.
 
You can try running the machine with the chain off as well and / or the clutch as well.
 
We're trying to narrow down the area...
 
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I removed the bar and chain.  Here is a video without the bar and chain

 
 
 
  youtu.be/HAj_sznFAmU