Saw won't idle down?

[Pioneer]

Here's something else you should check.



This throttle plate will never let a proper idle happen. Whether it's from wear or poor fit from the factory, the high bypass on the sides will create not only the high idle but mixture problems as well. The reason being there won't be enough flow at the bottom near the idle port where it's needed.

 

[trains]

Is the butterfly on the correct side of the throttle shaft, I see it milled flat this side, would not the butterfly fit up against that side of the shaft ?

have come across incorrectly "rebuild" carbs before with butterfly wrong side, upside down etc, and like you said, not enough air passing the idle drillings for it to tune right.

 

[Pioneer]

The butterfly shaft is actually slotted. It's probably milled flat so the screw seats properly.

 

[heimannm]

Did you try loosening the screw and centering the throttle plate? Whenever I have to remove/replace a throttle or choke butterfly I always find it necessary to fiddle a bit and get them properly located.

Mark

 

[Piotr Pakuła]

Or maybe the cause is an engine leak

 

[SteveSr]

Here's something else you should check.

View attachment 1172583

This throttle plate will never let a proper idle happen. Whether it's from wear or poor fit from the factory, the high bypass on the sides will create not only the high idle but mixture problems as well. The reason being there won't be enough flow at the bottom near the idle port where it's needed.

That plate looks to be installed incorrectly. Those dimples are supposed to line up on the shaft ad prevent rotation. Also most plates that I have seen are beveled for a tight fit when closed.

 

[ZeroJunk]

Unless it has an accelerator pump why would you take it out ?

And, yes they aren't exactly round. You need to remove that shaft to replace an accelerator pump and mess with it a little bit to get it right.

One of the failures with Chinese carbs is the butterfly sticking.

 

[Pioneer]

The plate is installed correctly. High side is spot on adjustment wise for the model of saw. Carb model is tillotson hs, I checked a walbro hdc I had lying around, it closes so tight it hardly lets any light pass through. Because the Tillotson has that notch in the bottom near the idle port the combination with the huge gap on the side just allows too much air through.
If the throttle plate didn't have the notch on the bottom, it probably would idle down. Checked other carbs I had lying around, none of them have that notch, not even a big walbro sdc.