Echo CS590 not holding Idle?

[wrighbr4551]

Hey all, me and my tech team, who are all new to 2-stroke engines, have been working on this chainsaw, that does not hold an idle. we have fully cleaned the carb several times in a sonic cleaner
adjusted idle screw
cleaned, then replaced air filter
we managed to adjust it to where it goes full throttle on idle, but there is no in-between. it either does nothing or idles with the chain at cutting speed. any ideas what else we could look at, or what else could cause it?

 

[ballisticdoughnut]

Check valve in carb could be bad/missing, torn intake boot, crank seal leaking, pulse hose leaking, etc. all that stuff needs to be checked.

 

[EchoShindaiwaMakitaDolmar]

Take a carb off a "known good" 590 and connect it- this will tell you if the questionable carb is the issue or not.

 

[vizette]

These models are notorious for carb issues - the check valve goes south and causes all sorts of issues (like ballisticdoughnut said). Pound it out and replace it. Should be about two turns out on both needles after that as a starting point. Just don't lean it out too much or it'll literally melt the piston.
https://www.arboristsite.com/threads/echo-590-timberwolf-h-setting.301438/page-6
If you can swap out another carb as suggested that'd be a quick validation too.

If it's erratic (racing, dying, etc), could easily be an air leak. Again as ballistic said, check the intake boot. If it's cracked or torn it can be hard to see at first.

Idles with the chain at cutting speed sounds like the "high idle" isn't kicking off. e.g. you pull the choke out, it also kicks up the throttle, and that should click off once you bump the throttle.

 

[ballisticdoughnut]

I’ve been through this with my 600P. I swapped the high speed nozzle for a non-jet type. Not because I want to rev the piss out of it but I wanted better control on the high speed. The HDA carbs seem to have a issue with check valves. My Poulan pro 330 had a missing check valve.

 

[Cliff R]

+2 Most idle issues with with HDA 268A carburetors will be with the check valve. This assumes that you correctly cleaned and rebuilt the carb with a genuine Walbro rebuild kit and have checked for leaks and verified the impulse hose is intact.

The Walbro replacement nozzles are available w/o a fixed jet so all the fuel to the saw comes from the "H" speed screw. They are only couple of bucks each and easy to install since they are grooved all the way around the feed passage instead of just a chamfered supply hole like the original jet.