Idle Tuning Chain Stop?

[Agoraphobia]

Was tuning the other day and wondered how many people tune their saws to idle with the chain completely dead stopped 100% of the time and how many have a little slow creep at idle? On my 660 there is quite a bit of adjustment between the two, so I wondered about any performance advantage of one verse the other. Or is the idling circuit irrelevant except at idle?

 

[MtnHermit]

Or is the idling circuit irrelevant except at idle?

That's my belief. It isn't a "circuit", simply opening the butterfly enough to keep the engine running.

 

[Agoraphobia]

So it's simply a matter of easy starting, good idling, and lack of chain rotation?

 

[JimQ]

Read through this. It might clear it up for you.

Q

http://wem.walbro.com/distributors/servicemanuals/WTseries.pdf

 

[Stumpys Customs]

THe idle (LOW or L) circuit is a separate circuit than the high side or H circuit hence two adjustment screws. Idle should be set a few hundred rpms lower than the clutch engagement rpm. The low side does effect the Wide open throttle mix since fuel is still being drawn through the low side into the venturi, but they should be adjusted separately. I adj the low side & idle speed first & the set the High side where I want it.

 

[Chris-PA]

That's my belief. It isn't a "circuit", simply opening the butterfly enough to keep the engine running.

That's not correct - there is a throttle prop, but there is also a separate idle fuel circuit with a separate needle to set mixture. The idle doesn't really matter too much once up to speed, but it needs to be set richer than would be otherwise appropriate because there is no accelerator pump (usually) to add fuel for acceleration. Also, even at WOT some fuel may be pulled out of the low speed port so I think it makes sense to set the H mixture last.

Sometimes my chains creep a bit at idle.

 

[Somesawguy]

I'm not a tuning expert by any means, but a little chain creep isn't a big deal for me. It's when it's idling high enough to be running the chain that bothers me.

That being said, any creep probably wears the clutch a bit since it's rubbing on the drum once in awhile.

 

[nmurph]

I don't like any chain creep, and it shouldn't if the saw is tuned to the factory idle spec. If it does, the clutch drum is dirty, the bearing is not turning freely, or the clutch springs are shot.

I tune the L, set the idle, and tune the H... and yes, on most carbs the L circuit feeds along with the H at higher rpm's.