Husqvarna 128cd String trimmer high speed running issue

[BBQGuy]

Husqvarna 128cd string trimmer Lowe's model purchased in 2017. Homeowner use only.
It started dying when accelerating. Suspected carburetor.
Replaced carb, all fuel lines, fuel filter, air filter, and plug.
Adjusted the low jet. Starts easily, idles fairly well.
Adjusted the high jet, once I got it to run wide open as it would die when accelerating.
With the unit warm and the edger attached, it will run for about 2 minutes and cuts off.
Once this happens, it restarts easily, but now abruptly dies when accelerating.
It takes several times in restarting and accelerating (as it dies during accelerating) before it will again reach high speed, but after about a minute at high speed its abruptly dies.
Have drained all of the fuel, remixed and still no improvement.
The fuel runs find in the leaf blower.
Spark arrestor is clean, no carbon in the exhaust port.

 

[bertsmobile1]

it can only die for 3 reasons,
too rich
too lean
no spark

so listen to the engine when it dies as they all have a specific sound.

When you adjusted the jets did you turn them too rich till the engine started to faulter then too lean till the engine just started to faulter and then back to sightly on the rich side of the midpoint between the two ?.

This is the way it must be done, starting with the HIGH needle then the low then repeat a few times till it accelerates smoothly.
If nothing else then you will be able to hear the different sounds.

If it is dieing rich the a full carb strip & rebuild is on the cards because the only thing that does that apart form a high needle too far out is a bad metering diaphragm or blocked return line.
If it dies lean then there are a dozen causes from bad tank pressure / venting to internal blockages or split metering needle.

The fastest thing is just to replace the carb with a known good one and if the problem persists then replace the grommet in the fuel tank and the fuel cap.

 

[primerbulb120]

It "abruptly dies" as in... sounds like you hit the stop switch all of a sudden? That's is an ignition issue. The 128LD/CD is notorious for such issues.

I would start by replacing the spark plug with a brand new OEM part (NOT a knockoff or "substitute" part.) Usual practice is to check the system with an inline spark tester before replacing anything, but I've found that on this model attaching such a spark tester usually causes the problem to suddenly disappear.

If a new, genuine spark plug does not correct the issue, try unplugging the stop switch. There's a plug on the underside of the trimmer with two wires (blue wires, I believe) that goes to the stop switch. With the stop switch unplugged, you can use the choke to stop the trimmer. I've had a few of those with intermittent ignition issues due to the stop switch failing.

If neither the stop switch or spark plug is causing an issue, it's the ignition coil (or coil wire, but they're both one piece.) If the ignition coil requires replacement, you may want to take it to a shop if your mechanical skills are limited. It's a rather involved repair and requires removing the engine from the trimmer.

On a side note, is the new carburetor a genuine Husqvarna part, or an aftermarket knockoff?

 

[BBQGuy]

Thank you for your replies.
OEM carb.
I’ll chase down the stop switch issue first as suggested. Have a friend the had anissue with his stop switch. If this doesn’t solve the problem then I’ll replace the ignition coil.

 

[AlaJim]

It "abruptly dies" as in... sounds like you hit the stop switch all of a sudden? That's is an ignition issue. The 128LD/CD is notorious for such issues.

I would start by replacing the spark plug with a brand new OEM part (NOT a knockoff or "substitute" part.) Usual practice is to check the system with an inline spark tester before replacing anything, but I've found that on this model attaching such a spark tester usually causes the problem to suddenly disappear.

If a new, genuine spark plug does not correct the issue, try unplugging the stop switch. There's a plug on the underside of the trimmer with two wires (blue wires, I believe) that goes to the stop switch. With the stop switch unplugged, you can use the choke to stop the trimmer. I've had a few of those with intermittent ignition issues due to the stop switch failing.

If neither the stop switch or spark plug is causing an issue, it's the ignition coil (or coil wire, but they're both one piece.) If the ignition coil requires replacement, you may want to take it to a shop if your mechanical skills are limited. It's a rather involved repair and requires removing the engine from the trimmer.

On a side note, is the new carburetor a genuine Husqvarna part, or an aftermarket knockoff?

What is the issue when an inline spark tester fixes the issue? The spark plug is clean and gap is right.

 

[bertsmobile1]

Plug is comprimised or the terminal at the end of the Spark lead is bad
Old mechanics trick to "fix" an oil fouled plug misfire was to pull the lead off then move it back till that cylinder started to fire .
Over a couple of minutes you move the plug lead closer to the plug till it runs with the cap on the plug.

The voltage at the spark plug does not arrive at the plug gap as 30,000V.
It slowly rises from whatever the low tension side of the coil is to full voltage then drops off back to zero if it does not jump the gap.

Everything on the planet has a particular resistance.
Dry skin is around 50 V which is why you can grab the battery terminals and not get zapped
So as the voltage at the plug gap it gets to the level where the resistance of tracking down the sides is less than the voltage at the gap so the electricity runs down the side & you get no spark

With the spark tester in line you have raised the resistance just high enough that the voltage arriving at the plug is high enough to jump the gap rather than track down the side .

back in the 60's there were all sorts of power boosters you plugged into the HT leads, either for each plug or just into the feed from the coil.
All of them were nothing more than a big gap for the electricity to jump so you got these massive 3" long sparks at the plug.
However they put a massive load on your coil which usually failed a year or two latter .
If your engine was old and suffering from oil laden plugs missing then they did delay the final death of the engine and they were popular with shonky used car sellers as they could sell cars with worn out rings that appeared to run well .

 

[AlaJim]

Thank you for the explanation. I'll start with a new plug and go from there. I still don't quite understand, but I've got some direction.

 

[BBQGuy]

Replace the coil.

 

[AlaJim]

Replace the coil.

Funny thing is, I just got finished ordering them. Do you know what the coil offset/clearance should be set to? Thanks for your response.