Tuning a Husqvarna 128LD trimmer

[MarkEagleUSA]

I just gutted the muffler on my unresponsive 128LD trimmer to see if I could get some more power. While a little louder, it seems a lot more snappy than it was. In reading the specs, Husqy calls for 2800-3200 RPM at idle which is no problem. They list Max RPM at 11,000 and Output Shaft RPM at 8,000.

Adjusting the carb with the aid of a tach, I can only get to about 8,400 RPM before the motor starts to really scream (lean?) and I don't want to burn it up. What's the proper way to tune a trimmer carb and should I really be targeting that 11,000 RPM?

In regards to the Shaft RPM, isn't that directly driven off the clutch (1:1) or is there reduction in the bevel gear at the head?

 

[MarkEagleUSA]

Anyone?

 

[JB Weld]

Being a jack-leg mechanic (at best), I have always tuned by ear (i. e. I cannot justify spending $$ on a tac). If you think it is screaming, you might be getting close to "too lean". It sounds like you really want to push the limit on this trimmer. Make sure it is 4-stroking a bit and then see where you are with the tac. One thing is for sure, you will know you are running too lean if you cook the piston.

 

[MarkEagleUSA]

Being a jack-leg mechanic (at best), I have always tuned by ear (i. e. I cannot justify spending $$ on a tac). If you think it is screaming, you might be getting close to "too lean". It sounds like you really want to push the limit on this trimmer. Make sure it is 4-stroking a bit and then see where you are with the tac. One thing is for sure, you will know you are running too lean if you cook the piston.

It's not that I want to push the limits... I just want it to be a little more responsive and gutting the muffler certainly helped. It stops 4-stroking at around 8400 RPM, or at least that's what it sounds like to me.

I guess I just need to know whether a trimmer would be tuned the same way a saw would be. If so, then I guess 8400 RPM is all I'm going to get from it.

 

[JB Weld]

It sounds like you figured it out!

With that 11k rpm, I bet that is under the best circumstances (i.e. the trimmer is new) and it is not really a speed meant to be maintained.

It is easy to forget about the muffler. One time I had a buddy hand me a 11 year old Homelite trimmer that had a hard life. He asked me to see if I could get it running. He had just given me a couple of chainsaws, so I said I would try (with an eye roll). I was in a situation like you described in your OP. I tore it all down and finally had it running, but I could not get any kind of WOT. So I just laid it on the bench and left it alone for a day. The next time I picked it up, I noticed how dirty the muffler was. It was crimped together, so I just fired up my fish cooker and laid the muffler in the flames. It smoked like a choo-choo train for about 20 minutes. Once it cooled off, I put the trimmer back together and she fired right up and ran like a champ. My friend was pleased as punch to have his favorite weed eater back in action. I have BBQed several mufflers on various two stroke engines. Here is a muffler off of a 82 Yamaha G1 golf cart. Look at the flames shooting out of the pipes. It had 30 years of oily crud inside of it. Man did it ever make a difference in how my cart ran.

 

[KenJax Tree]

I have a 326LS that is a few years old, I'll check it on my tach....i've never tuned it by tach just by ear so idk what rpm's its running at. I'll let ya know[emoji16]

 

[KenJax Tree]

You have something wrong with your trimmer

 

[HuskStihl]

I've got a 326ls as well. Never thought about taching it, but definitely gutted the cat muffler. I tune it so that when the line is at full length, it barely 4-strokes out of the grass. As the line wears, it 4-strokes sooner. Muffler modded, it's a surprisingly strong trimmer.​

 

[KenJax Tree]

I did the same thing.

 

[MarkEagleUSA]

I tune it so that when the line is at full length, it barely 4-strokes out of the grass. As the line wears, it 4-strokes sooner.

That's essentially what I did since I wasn't sure if tuning it like a saw was the proper way. I probably kept it a little fat since I was unsure and didn't want to burn it up. When I checked with the tach I noticed that was only 8400 RPM. Since the tech specs say max RPM is 11000 I questioned the difference.

The trimmer is only going on it's 3rd season and I used regular fuel mix the first season. Last year was 40:1 TruFuel only. I'll pull the carb and have a look there.

Maybe this is the best to expect from this trimmer.

 

[MarkEagleUSA]

It sounds like you figured it out!

Well, I haven't toasted it yet at least.

sy to forget about the muffler

When I separated the muffler it had a bit of oily, gunky residue inside that I burned off with a propane torch. I also completely removed the center baffle with the catalyst and opened up the opening.

I know it's just a trimmer, but I'll be using it as a pole saw over the next couple of weeks and just wanted to give it a bit more power if possible. For that I thank everyone here at AS!

 

[Miles86]

Hey-

Your 11,000 rpm is no load rpm without a trimline head installed . Tune the trimmer to 8000 with trimline head installed and trimmer line out to max length (to line cutter). This is the max loaded rpm, if your at 8400 rpm your 400 rpm lean.

 

[MarkEagleUSA]

This is the max loaded rpm, if your at 8400 rpm your 400 rpm lean.

Even with the muffler opened up? It still burbles pretty good at 8400.

 

[KenJax Tree]

Hell mine 4 strokes so hard its barely running at 8500 rpm....it just cleans up at 10500.

I doubt you lose 3000 rpm with the head and line on it.

 

[HuskStihl]

If KenJax is still talking about his 326, it is a completely different animal than the 128. Think 346 vs 455

 

[Deleted member 83629]

i got a 223l with a 323l shortblock muffler modded its a mean trimmer my trimmer has enough grunt to hang with a stihl fs 90 4 mix.