Metering lever arm was set a bit too low.
chainsaw repair question craftsman saw
- Thread starter Subieman406
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Subieman406
Saw ID10T site lurker
It was a obvious fix just got overlooked but it was a fuel needle valve arm in the carburetor saw would run lean and then rich varying rpms and turn out the height of the needle valve arm was off saw runs like a champ now little wore out thou in the cylinder but no scoring just really used
Subieman406
Saw ID10T site lurker
the saw would peak out from idle to full rpms then drop rpms go back to idle and right back to full rpms at full throttle then drop rpms of again vary lean dangerous lean seize territory. No harm to piston and cylinder thou so wasn't metering the fuel right that's all
old 040
Addicted to ArboristSite
i believe what he meant was metering arm lever, not needle valve lever was too low....................
The metering lever controls the inlet valve to the fuel chamber (equivalent to the fuel bowl on a float carb). It needs to be set such that the spring pressure is strong enough that the fuel pump or pressure in the tank cannot force the valve open, but weak enough that the diaphragm can push it open. Between those limits it does not matter too much. Bending the metering lever effectively changes the pressure on the spring.
If the lever is too low the spring is effectively stronger, so the diaphragm might not be able to over come it and the engine starves for fuel.
I suppose in theory you could also have mechanical interference if the lever is recessed too far, or some situation like that.
Thanks for you explanation. I understandand the operation of the lever which is why I'm not grasping how this would have caused a fluctuating rpm.
Set to high or low (in my mind) would result in an absence or abundance of fuel. Not a combination.
Set to high or low (in my mind) would result in an absence or abundance of fuel. Not a combination.
dswensen
ArboristSite Guru
Nope, not your reading. It was the lack of punctuation. I read it 4 times and still didn't get it. Had to read it out loud the fifth time, and then finally understood.
ethar
ArboristSite Operative
Have you ever got your vehicle where it was about to run out of fuel. Won't happen too often with fuel injected but the old carb cars alot of times would surge. This is a result of too much air not enough fuel. Air don't run out so the carb will keep sucking in air causing a leaning of the mix. Same deal with the metering needle being set wrong either it will flood of lean out. At idle it can run fine but when the is revved it starts using fuel is when it acts up. I can tell when my Mac 10-10 is fixing to run out of fuel by this method.
