Well, it's used near the house so it's only a little OT. Anyway, it
starts and runs fine when cold. But as it warms, the RPMs continually
increase until it is running extremely fast. The visual problem is
that the carb throttle plate is against the idle adjustment screw when
cold, but when hot the plate never returns to the idle screw. When
turned off, it immediately returns to the proper position. The
throttle cable is clean and loose. The throttle plate has a coil
return spring that has been cleaned and lubed. All fuel lines have
been replaced. So the problem doesn't appear to be anything sticking,
rather sucking fuel/air faster than the spring can overcome. There is
no apparent vane governor like mowers have. Any ideas out there?
BTW, it,s a Husqvarna Mondo.
I'm not aware of governors on these smal engines. Usually the
throttle cabel is directly connected to the carb throttle plate. At
least that's the way all of mine are. Sounds like your throttle cable
It doesnt make sence, have you tried moving it by hand when hot,
something is holding it up, air flow shouldnt be strong enough unless
its maybe a bad spring or disconnect the cable, run it and move it by
hand and see.
Not making a lot of sense to me either, that's why I'm looking for
ideas. When hot, I can move the throttle plate back in contact with
the idle screw and the RPM's return to normal. But as soon as I
release it it speeds back up.
On mine, the solution would be to adjust the throttle cable. Without
the plunger on the end of the throttle cable to hold the throttle lever
closed, the running motor will suck the throttle open. The throttle
spring on the carburetor holds it closed only until it starts. In your
case, apparently the spring holds it closed until it warms up.
I don't see any way to adjust the throttle cable. The housing has
molded ends to fit in slots, and the cable itself has permanent
fixtures. I tried sliding the trigger housing back & forth to change
the slack in the cable but that didn't change the problem.
I imagine that when the throttle is released, the throttle linkage
should push the throttle closed.
A couple of years ago I borrowed a Husqvarna chain saw that sometimes
ran much too fast without my hand on the throttle. A screw fastened the
throttle actuating arm to the carburetor. It was loose, allowing the
throttle plate to turn independently of the arm.
Not perceptably. The throttle trigger has it's own return spring that
keeps it from moving without finger pressure. That adds to the
confusion since a return spring at the trigger and another one at the
throttle plate appears to be more than enough to keep this from
happening. The throttle plate is bradded to the carb shaft rather
than with a screw so that is not the problem. The more we talk this
thru, the more it sounds like an air leak. I'm going to tear it it
all down and reassemble tightly.
You may not have to tear it all the way down. Just tighten everything
up first and see if there are any loose screws/bolts. I've done this
before and it is better than tearing it all apart. You may have to
remove a shroud or something to get to all the srews that hold the
If the trottle trigger is not moving when the plate is opening you
have something in the path loose. Otherwise you would see the trigger
move. Since it normally relys on a spring at both locations this is
why the one at the carb is not enough.
It should be simple to put one hand on the shaft lever where the
throttle cable attaches and hold the trigger with the other hand. Now
try to move one while holding the other tight. Should not be a lot of
play in something this simple. If you've got a lot of play then you
need to figure out where it's happening.
That was my last idea. I have a new carb-to-block gasket on order but
I don't have a lot of confidence that will solve the problem. I'm at
the point of just eliminating possibilities. Shotgunning in other
Well, back to square 1. All carb and carb mounting screws were
tight. There is nothing at all wrong with the throttle cable. The
throttle plate spring tension measures 20oz in the direction of
throttle cable pull. (Not sure what it should be but that seems like a
fair amount to me.) The carb-to-head gasket I have ordered may not
get here for a long time b/c Husqvarna parts distribution is almost
nonexistent right now. Besides the gasket is not in that bad of shape
and I applied a thin coat of gasket sealer to seal minor
Am I even looking at the right direction? I haven't rebuilt the carb
since it runs smooth. Normally a carb will stop up rather than pump
excess fuel. Or will it?
Look closely at the throttle cable, one square end may not be molded on,
but actually screws on. (not the metal thing that goes into the throttle
plate or trigger but the part that locks in a recess to hold the cable
in place) If so, unscrew it so you can trim the outer shield approx 1/8"
shorter & screw the end back on. This will allow it to idle.
HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.