OT: Weedeater problem


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.
KC
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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 is disconnected.
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Nope, it's connected. As I said everything works right when cold.
KC
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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.
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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. KC
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KC wrote:

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.
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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.
KC
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KC wrote:

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.
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I agree, something loose somewhere along the throttle controls.
Do you actually see the throttle trigger moving when it does this?
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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.
KC
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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 case together.
Hank
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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.
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jamesgangnc wrote:

The arm on the throttle shaft has two holes. If the throttle is hooked to the hole nearer the shaft, I imagine that could allow the throttle to be sucked open a little without cable movement.
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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.
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You might have an air leak. Tighten all the screws/bolts on the cylinder/jug/carb and etc.
Hank
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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 words.
KC
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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 imperfections. 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?
KC
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On 6/25/2010 8:07 PM, KC wrote:

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.
MikeB
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