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Mower Problem

To: Shop Talk <>
Subject: Mower Problem
From: Mike Frerichs <>
Date: Mon, 27 Mar 2000 21:36:29 -0600
Anybody know anything about small engines?  (I know, silly question to
ask on this list!)  Specifically, a two year old Lawnboy 2-stroke (it's
always had the proper gas/oil mixture).  Last fall it was starting to
run a little badly and the engine speed was starting to fluctuate.  I
figured I'd wait till spring and clean the carb and that would be that.

Well, Saturday I took the carb all apart and cleaned it inside and out
(mostly out, because the inside was very clean already).  The main
(only) jet was not clogged at all.  I put it all back together and
cleaned and oiled the air filter.  When I started it up it seemed to run
perfectly (no missing or coughing) but the speed continuously goes up
and down.

There is what I guess would be called a governor, which is composed of a
blade that sticks up into the air flow of the fan on the top of the
engine.  This blade is attached to a butterfly plate at the end of the
carb that mates to the engine.  The faster the engine runs, the more the
air pressure pushes the blade in a direction that closes the butterfly.
There is also a coil spring around the shaft at the base of the blade
which tries to push the blade in the opposite direction of the air
pressure.  I think the manufacturers intention is for the spring and air
pressure to find a balance and produce a steady running speed.

My question is, why can't my mower find a steady speed to run at?  The
governor blade is continuously moving back and forth, and thus the rpm's
go up and down.  If I adjust the spring a little tighter, the rpm's go
too high and won't come down until the throttle is closed almost all the
way.  If I adjust the spring looser to where the rpm's level out, the
top speed is way too slow.

I know this is probably something simple, and the repair shops around
here are backed up for a couple weeks.  Can anyone help me out?


Mike Frerichs
(Great with cars and motorcycles - just can't understand mower and
trimmer engines!)

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