Husqvarna 128LD Will Not Stay Running

[DerekF]

Alright so let me run you through everything I have done to my dads Husqvarna 128LD.

First Round -
Clean the aftermarket carb my dad put on it last year.
Cleaned air filter and oiled it.
Used original gas lines and new ones of different size (thought the ones on it seemed a little on the big side for the little pipes coming out the carb).
Checked spark plug - practically brand new.
Cleaned spark arrestor.
Other greasing and cleaning that needed done

Second Round -
Put on new OEM carb.
Tried original fuel lines, new fuel lines of both the same diameter and a smaller diameter from the old ones.
Removed spark arrestor completely.
Put in fresh, ethanol free, 40:1 mix gas that works great in my chainsaws.
Tried running it with and without air filter.

Neither time did this weed eater have a fuel filter on the hoses.

HERE IS WHAT IT IS DOING -
I go through the suggested starting sequence. It seems to do ok but once I turn choke all the way off and its warmed up, I pull the throttle and it begins to rise in RPMs and then just bogs down and dies. It runs a little rough as it is. What could be the problem? I am stumped!

 

[ILENGINE]

The OEM carbs are set from the factory to get it to start, but most of the time will need properly adjusted to run right. I am assuming this is the cube type carb with the recessed spline type adjusters correct. The adjuster wrench is out there but don't ask a dealer to sell you one because he can't.

 

[Darryl G]

So there's no fuel filter on the line? Is the fuel line floating?

 

[AVB]

As ILENGINE said these carbs are sent only tuned to a will start setting and must be tuned once installed. Also since you have been running the trimmer without a filter you may have clogged the carburetor's internal filter screen. It is a backup filter screen in case someone runs the engine without a filter and does plugs fairly easily. This to prevent internal clogging of the carburetor fuel passages. Depending on which version of this screen you may need to replace it as one version is not cleanable.

 

[DerekF]

As ILENGINE said these carbs are sent only tuned to a will start setting and must be tuned once installed. Also since you have been running the trimmer without a filter you may have clogged the carburetor's internal filter screen. It is a backup filter screen in case someone runs the engine without a filter and does plugs fairly easily. This to prevent internal clogging of the carburetor fuel passages. Depending on which version of this screen you may need to replace it as one version is not cleanable.

I haven’t been running it without a fuel filter. It has brand new oem carb on it and it didn’t work from the beginning.

The trimmer behaved the EXACT same way with two different carbs on it.One cleaned by myself, one brand new.

I am going to go out on a limb and say it is not carb related.

 

[Hammermechanicman]

Have you removed the muffler and checked the piston for scoring?

 

[DerekF]

Have you removed the muffler and checked the piston for scoring?

This is my next step.

 

[AVB]

PNC scoring normally affects the starting ability first as it lowers the starting compression below 100 psi.

With me repairing over a couple hundred these cubes what you describing is a lean burn problem; and unless, you re-tune the carburetor you never get it to run right. I see no where you have mention you tried tuning either carburetor. of the hundreds of cubes that repaired only one chainsaw with airhead carburetor had PNC damage that would allow it to start but not accelerate once tuned.

Now there is one other possibility not mention here in this thread and that is that the spark arrester could be clogged with can the similar symptoms as I have seen engines to start on choke then would run good at idle but fall flat on opening the throttle. Stilh 2 cycles are especially bad about this as they run richer than most 2 cycles.

On cleaning the carburetor how did you clean it; hopefully not with carburetor cleaner? They should only be cleaned using an ultrasonic cleaner with soap and water. Plus it preferable that the mixture screw(s) are removed to allow deep cleaning of the mixture passages. No probing allowed or excessive air pressure as it damages delicate check valves inside the cube. Even the carburetor cleaner can damage the rubber check valves. Then once a carburetor repair kit is installed the metering lever must be set to the correct height and both mixture screw lightly seated and out CCW 1-1/2 turns for the will start setting with fine tuning once the engine starts. L mixture is tuned first and then H mixture as they do interact with each.

Even a brand new OEM carburetor may need to be reworked too as I have seen the metering lever set incorrectly from the factory. Plus aftermarket carbs at one time were terrible and most still are about not working correctly. I got an aftermarket for a Stihl backpack blower that both mixture screws have absolutely no effect as they never was fully drilled.

 

[DerekF]

So let me update you all. Forget everything I posted above.

This weed eater is starting just fine. Idling OK. and when given gas it slowly (slower than I think it should) revs up. It hits a certain audible RPM sound and then bogs out and dies. There is no saving it when it does this. You cannot pump the throttle, you cannot take your finger off the throttle. It just simply dies. It did this with both the old and the new carburetor. Exact same RPM, exact same timing, everything.

What I have done to it.

1. Brand new OEM carb. Misbehaved the EXACT same way as the aftermarket carb on previously before.
2. Muffler has been totally cleaned as well as spark arrestor that has been completely removed (worked the same as before it was off, same as after it was clean, same as after I completely removed it).
3. Brand new fuel lines.
4. Brand new fuel filter.
5. 102 PSI of compression.
6. Fresh ethanol free gasoline with a 40:1 mixture. I'd rather run it a little richer than to lean (I believe it calls for 50:1)

I checked the cylinder the best I could while the muffler was off. It looked good.

I am not a small engine mechanic. Obviously. I pretend to be one. I have never ran into an issue I couldn't at least diagnose what the problem likely is. This is getting beyond frustrating and at the same time, killing my pride of being a pretty dang good handyman.

I will look into getting the tool to adjust the carburetor. Again I am not a small engine mechanic, but I just feel like this is not the solution, but am totally open to trying it.

Thanks to everyone who has replied so far.

EDIT: I ordered a carb adjustment and cleaning tool kit on amazon. It came with like 8 different carb adjustment tools and some cleaning rods and brushes for like $12. Has the husky tool in the set.

 

[ILENGINE]

Some remote thought. If this had the newer style variable ignition timing module with the built in rev limiter you could have a faulty ignition module also that could cause weird symptoms. Nothing like fighting a faulty module that never looses fire,but in your cause you could be loosing fire above a certain rpm.