ms 250 idle issue

There are two adjustment screws that affect idle: mixture and idle speed. To set the low-speed mixture screw, turn it all the way in (clockwise) and then back it out one full turn, then fine-tune it until the saw idles smoothly and accelerates well. Then, adjust the idle speed screw so that the chain doesn't move when the saw is idling with the brake disengaged.

All of the above assumes the saw is otherwise in good working order. If it's difficult or impossible to get it to run right by making those adjustments, something else is likely wrong.

Some Choices: 1. Disassemble carb and clean, looking for dirt in screen and stiff diaphragms. I'd have a carb rebuild kit ready - cost $2.75 from China.
2. Buy a new AM carb with both H-L mix screws for $10 (China).
Search ebay "MS 250 carb" - maybe Canada has similar.

A carb rebuild or replacement isn't a guaranteed fix, but it's a fairly cheap and easy next step since you probably don't have a vacuum or pressure gauge.

Curious...was it sitting for a while with gas in it?

SKIN052 said:

I have a compression gauge. What pressure should I read?

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It should have a Schrader valve. Pull multiple times and look for something around 150 psi.

How to check your fuel line:

I have the same saw. Now, I'm no expert and I doubt this anything to do with it, but there's a plastic plate by the air cleaner somewhere that can be adjusted for winter or summer. I never changed mine for years, so, like I said, I doubt that'll fix it, but...