Need Zama Carb Expertise - Main Nozzle Check Valve

[SteveSr]

Usually leaky check valves make them hard to start, although it could cause running problems at low rpm I suppose. However, a leaky check valve won't hurt high rpm at all, as the check valve is open then. So given the symptoms I'm guessing that the check valve is a red herring.

Well, I guess it would depend on the amount of "leak" the symptoms that are observed. My observations tend to support @Old2stroke 's observations as well. The saw idles high or stalls and won't transfer to the main nozzle circuit. This sure sounds like a sticky main nozzle check valve bleeding too much air messing up the low end and failing to transfer to the main nozzle.

 

[SteveSr]

And by the way...check valves going bad will still operate at wot.

Yes, If you can get them to transfer to the main nozzle circuit. On the 210 I couldn't get it to do this even "babying" the throttle. But it would still idle... fast and would occasionally stall at idle too.

 

[Chris-PA]

Well, I guess it would depend on the amount of "leak" the symptoms that are observed. My observations tend to support @Old2stroke 's observations as well. The saw idles high or stalls and won't transfer to the main nozzle circuit. This sure sounds like a sticky main nozzle check valve bleeding too much air messing up the low end and failing to transfer to the main nozzle.

Use a little choke to get it up on the H circuit - once there the check valve is irrelevant. Or won't that master control lever thing allow you to do that (I don't know Stihls)?

 

[Chainsaw Jim]

Yes, If you can get them to transfer to the main nozzle circuit. On the 210 I couldn't get it to do this even "babying" the throttle. But it would still idle... fast and would occasionally stall at idle too.

Just buy a new carb. It isn't worth all the hassle. A new one is only a couple dollars more than a new kit. It will cost less than replacing other carb parts and they're plug and play.
Then if you want to experiment for diagnosing the old carbs you can do so while you have a working saw.

 

[Pietro Minucci]