Stihl 041 Farm Boss rebuild issue

[rslee]

I just recently rebuilt my father’s old Stihl 041 FB. New head, piston, rings, cleaned carburetor, and replaced the crank seal on the clutch side. I did not split the case. I have the flywheel puller tool on the way and will replace the seal under the flywheel when I can. I decided to throw it back together to see if it would run out. I have to set the low speed only at 1/4 to 1/2 turn out to crank, and I can’t idle it down enough to stop the chain from spinning without it stalling. I would expect if the crank seal was leaking, I’d have to be running out the low speed screw more like 2 turns instead of only 1/2 to compensate for the leak. I will try to pressure test and vacuum test it if I can pick up the equipment. Thoughts on what would cause it to want to be set so lean? Should I be thinking carburetor rather than air leak? I definitely don’t want to fry this new top end.

 

[stihltech]

Continue with the diagnosis. Spray some brake clean near the seals. If the idle changes, seals may be the culprit. Remember the seal in the center of the pump worm.
So many spots on an 041 to cause issues. Intake gaskets and oil pump seals. Carb too rich? Inlet needle leak, inlet lever high, welch plug leak, pump diaphragm leak. Metering diaphragm dislodged from forked inlet lever (if equipped). I always sand the bottom of the intake riser to ensure a good gasket (2) seal. Don"t forget to time the points.
This is where I started. Great saw when sorted out.

 

[preventec47]

Continue with the diagnosis. Spray some brake clean near the seals. If the idle changes, seals may be the culprit. Remember the seal in the center of the pump worm.
So many spots on an 041 to cause issues. Intake gaskets and oil pump seals. Carb too rich? Inlet needle leak, inlet lever high, welch plug leak, pump diaphragm leak. Metering diaphragm dislodged from forked inlet lever (if equipped). I always sand the bottom of the intake riser to ensure a good gasket (2) seal. Don"t forget to time the points.
This is where I started. Great saw when sorted out.

I have my dads 041-AV without any vibration absorbtion on the handle with only 30 or 40 houirs
on the motor. Was sitting in my dads garage for 45 years and had oil in the cylinder. About 15 years ago I took it to stihl dealer for overhaul and the repair cost was more than the cost of a new Sears chainsaw so I never had it repaired. I remember using it at age 14 and 15 and how my hands were numb after an hour or two of using it. I thought maybe someday I would have enough time to overhaul it myself but I see now it is never going to happen.

 

[Patrick1903]

Take a look at this link and use the search for other 041 threads. The link shows the 12 common areas of air leaks on 041s. I rebuilt one last year (top) and chased issues until I replaced the oiler o ring and seal. Different than your lean issue though. I was getting oil fouling I believe. My thread is on this site.

https://www.arboristsite.com/threads/041-problem-and-theory.261143/