Small Engines (Lawn Mowers, etc.): Toro 521 hunting/surging idle., toro 521, tecumpseh

Question
First off, this site is GREAT! Thanks to all who volunteer their time to answer ?'s!!!

I recently cleaned out a stale, green-varnished Toro 521 Tecumpseh fuel system, and got it from dead to running. I took the bowl off and de-varnished all needles, bowl, float, both passages in the main valve assembly with tag wire, tightened carb to manifold bolts, and reset the main and idle mixture screws to 1-1/2 turns out.
The problem is a severe hunting/surging. The governor is free, and swings wildly to the beat of the full spectrum of rpm ranges! Most likely still varnish in carb passages? Can you provide more detail in cleaning carb passages with tag wire, so often mentioned on this site? Like what passages and where are they located inside the carb, etc.? I'm assuming there are different passages, other than the two small holes in the main valve, that need attention? Can anything else be causing this severe of a hunt in rpm? The snowblower will drive the wheels, turn the augers, and throw snow, but does not give the impression that it is a smoothly running repair for my customer.
Thanks much, Bill.


Answer
Hi Bill,

Hunting is usually caused by a weak governor spring.  It could also be caused by irratic fuel flow.  You mention 1 & 1/2 turns out on the jets.  That's correct for the high speed jet but the low speed jet should be at 3/4 turn out.
 
Check those areas and let me know how you make out.
Michael

The passages vary so much from carb to carb that it would be hard to give an exact description.  Just look the entire carb over and with a piece of tubing blow into each opening to verify that you have an open passage.  Check the float level setting too.