Echo 500 EVL Idle Quirk

[Wood Doctor]

This quirk has me stumped. I restored a classic old Echo 500 EVL's carb that was running the engine very poorly. It now starts and runs at top end smoothly. Acceleration and power are both fine. Resting on the ground or on a table, it idles perfectly and the chain loop is at rest. When you pick it up by the outer handle, it suddenly adds about 150 RPM or so, just enough to trigger the clutch to start the chain moving. Set it back down, and the RPM slows immediately to the correct idle speed, slow enough so the chain does not move.

I have never run into this with any other saw that I have worked on. and I own an identical saw that does not do any of this. I've tried adjusting all the setscrews (idle, lo and hi) with no luck, so I adjusted those back to the factory recommended settings. Any idea what is causing this strange behavior and/or what I can do to fix it? TIA.

 

[Wood Doctor]

A thought came to mind. If a simple lift of the saw vertically adds air to the fuel mixture somehow, that could cause a slight rise in RPM. If so, how is that air getting into the fuel mixture? Crank seals? And, if it is air getting through the seals, why would a simple vertical lift of the saw cause that?

 

[TLG]

Isn't the intake manifold secured to the top cover/handle ass on that saw. And it moves separately from the crankcase if I remember correctly?

 

[telecasterfool]

I had a similar situation once, it was loose screw causing the throttle linkage to move slightly. Check to see what moves when you gently apply pressure up on that handle. The RPM change you are seeing doesn't take much air - very little. good luck

 

[Wood Doctor]

Isn't the intake manifold secured to the top cover/handle ass on that saw. And it moves separately from the crankcase if I remember correctly?

I checked. There is no movement of the top cover and it is secure. Lifting up on the the outer handle to carry the saw will increase the RPMs just enough to start the chain moving. The throttle control and/or linkage does not budge. Setting it back down down on any stable surface restores the lower idle speed. It simply makes no sense to me. This is the only saw I have ever seen or operated that does this.

Not sure how this can help, but here are a couple of saw Pics: