Jonsered CS2240S runs only at WOT

[Deanpeddle]

Jonsered CS2240S  (same as Husky 435 I'm told).  This saw has served me well over the past 5 years.  Recently it started 'racing' while in idle.  I adjusted H / L and Throttle to get it usable for a few minutes but then it acted up again.  So now the saw will start easily if choke is on but won't idle. If I feather the throttle a bit I can get it to WOT (11500 - 12500 RPM on tach) and it will keep running as it should. Once its running (i.e. just about WOT), as soon as I let her throttle down (say somewhere between 5500 and 7500) she cuts off. Carb is not the problem as I tried another carb and got same issue.  My first thought is/was an air leak ... but not sure - esp. since she's 'normal' at WOT.   How can I confirm that an air leak is the problem? Should I start with replacing fuels lines, purge bulb, stuff like that? any suggestions welcome.

[sawguy21]

Welcome! You could start by blindly throwing parts at it but a can of carb and choke cleaner is cheaper and easier. Spray i around the base of  the carb and over the fuel line, a change in running will indicate an air leak. With the bar and chain off, do the same behind the clutch. There may be debris disturbing the seal.

[charles mann]

My 2166 had a bad carb causing near the exact same issues. Put a new carb, drained the pump gas the shop filled it with and serviced with a tank of avgas. No issues in 2 yrs