Chainsaw Repair

Did you mess with your I - Idle screw?  Try backing it off. 

Then see. Then try going with the L screw from lightly seated to 1.5 turns out and see.

Just curoius do you have the carb with the H side too?   

New carbs with fully adjustable H and L sides are only $30-$35 from stihl.

Clockwise till lightly seated.  Then turn counter clockwise out to 1.5 see what you get.

If not carb and put together wrong if you took a[art to rekit etc.  Could be a air leak.

Have you checked your impulse line for cracks etc.  From back of carb area to back of crankcase cylinder area.  https://www.sawagain.com/stihl-021-023-025-ms-210-250-impulse-line-11231418600/?gclid=EAIaIQobChMI_KrHo7n-6AIVB9bACh0k1gJoEAQYASABEgJnKfD_BwE

Someone else posted this so no need to re-describe = (((((((  The impulse line is hard to get to and hard to see. But you can get to it from the left side (bar pointing forward), under the recoil cover, just above the coil and behind the flywheel. The impulse line goes from a metal nipple at the back of the engine to a plastic nipple in the orange handle that leads to a hole in the carb just to the side of the intake port.

So, take off the recoil cover, find the line, and use needle nose pliers to dig around in there to pull that thing out and shove another one in there. It can be done. Take your time. or take the entire orange handle off (another PITA on these saws, requires removing carb and other stuff) and pull the intake boot off and there it will be, exposed  I have done it both ways, and recommend the first.   ))))))

Video online might help you

https://youtu.be/GY5MRPBscnI