Stihl 026 sometimes starts super hard and sometimes loses power at WOT

[SteveSr]

Hey guys. Went to my Stihl dealership and brought in my carb. I have the walbro "WT403B" carb on my 026. I asked the dealer to get me a rebuild kit, he said no such thing from Stihl. I see what appears to be aftermarket ones, like this one: https://www.ebay.com/itm/314010067868 - reasonable to get one of these? if not, what do you suggest?

The Stihl dealer said they'd gladly sell me a new carb for $80.

Is this the non-adjustable "H" version? If it is the one that I am thinking of it seems to exacerbate the fuel pooling in the intake issue. I throw them away and replace with a fully adjustable WT-426.

 

[gary-stihl]

Is this the non-adjustable "H" version? If it is the one that I am thinking of it seems to exacerbate the fuel pooling in the intake issue. I throw them away and replace with a fully adjustable WT-426.

No "H" adjustment that I can see; I don't see any adjustment for that matter.

 

[gary-stihl]

Hey all, I got the rebuild kit, and applied it to the carb, after cleaning the whole thing out.
I did notice these adjustments (see pic). "LA" I assume is low idle. Easy enough to figure out.
the "H" and "L" - whilst labeled, there exists only one adjustment in the middle slot.
Is this H only? What should be the starting adjustment? I turned it all the way in, then backed it off 1 full turn.

I got'er started, took a little bit, and it seems to do ok at WOT, but need to test it more (rain stopped that).
What it doesn't do is idle. Stalls out, then i need to choke it to restart. Is this a matter of cranking in the LA screw way more?

 

[SteveSr]

Hey all, I got the rebuild kit, and applied it to the carb, after cleaning the whole thing out.
I did notice these adjustments (see pic). "LA" I assume is low idle. Easy enough to figure out.
the "H" and "L" - whilst labeled, there exists only one adjustment in the middle slot.
Is this H only?

This is the "L" screw

What should be the starting adjustment? I turned it all the way in, then backed it off 1 full turn.

Correct.

I got'er started, took a little bit, and it seems to do ok at WOT, but need to test it more (rain stopped that).
What it doesn't do is idle. Stalls out, then i need to choke it to restart. Is this a matter of cranking in the LA screw way more?

Possibly. Did it idle before you started messing with it?

 

[gary-stihl]

This is the "L" screw


Correct.


Possibly. Did it idle before you started messing with it?

Yeah, idled fine. I did mess with that screw. If anything, I can turn it in a good amount and if it is idling too crazy, back it off

 

[Oldman47]

Yeah, sorry, my phone doesn't have a macro mode (iphone 13 mini) so hard to get close-ups. The piston did look smooth.
See picture I just posted of exhaust screen, not clogged, near as I can tell?

For oil, I use the 2 cycle oil for marine engines (used to have a 2-stroke Force 70HP) mixed with 93 octane gas (unfortunately, ethenol-enriched; sometimes I can get lucky and get real gas). I'm pretty careful with the measurements of oil : gas, 2.6oz oil to 1 gal of gas. Use this for my other two cycle engines as well (a few echo leaf blowers, weed whacker, and i have a Stihl 036 that runs super strong and never have an issue). What could be causing the carbon buildup?

Marine 2 stroke oil is not the same as the chain saw 2 stroke oil. That may be a small part of your issue.

 

[Elk247]

Do I need to remove the carb to find the number? I am thinking "yes" to that question.

Maybe you do. It’s stamped opposite the jet side. Probably just have to remove the fuel line and you’ll see it.

 

[gary-stihl]

Hi friends. Welp, i got the carb all rebuilt with the Walbro kit, cleaned out air filter, exhaust port, new spark plug, new 93 oct gas with the stihl oil (I know, not the best, once that is gone will pivot to the other oil someone mentioned). she fired up a bit hard on the first startup, but after that not bad. At WOT, runs without bogging down at all. Seems to be running good and strong.

The problem remaining now is if i set the saw down, it will idle for a bit, and eventually stall out. OR, if i pick it up before it stalls and hit the throttle, it bogs and stalls, simetimes i can get'er to rip if I 'feather' the throttle a bit. For restarting, i can't just start at idle, have to choke first, then it'll start. I attached a recording, maybe that helps explain.

 

[muddy42]

Hi friends. Welp, i got the carb all rebuilt with the Walbro kit, cleaned out air filter, exhaust port, new spark plug, new 93 oct gas with the stihl oil (I know, not the best, once that is gone will pivot to the other oil someone mentioned). she fired up a bit hard on the first startup, but after that not bad. At WOT, runs without bogging down at all. Seems to be running good and strong.

The problem remaining now is if i set the saw down, it will idle for a bit, and eventually stall out. OR, if i pick it up before it stalls and hit the throttle, it bogs and stalls, simetimes i can get'er to rip if I 'feather' the throttle a bit. For restarting, i can't just start at idle, have to choke first, then it'll start. I attached a recording, maybe that helps explain.

You should also replace the fuel filter as its cheap and removes another potential problem area. Check all the tubes and lines for cracks or leaks with pressurized air.

This could be just a tuning issue, have you set the carb to factory default settings? Do this and then tune from here (plenty of advice online about this). If this doesn't help and you cannot maintain tune, you have something else wrong. I'd move on to checking the cylinder for an air leak.

 

[SteveSr]

Hi friends. Welp, i got the carb all rebuilt with the Walbro kit, cleaned out air filter, exhaust port, new spark plug, new 93 oct gas with the stihl oil (I know, not the best, once that is gone will pivot to the other oil someone mentioned). she fired up a bit hard on the first startup, but after that not bad. At WOT, runs without bogging down at all. Seems to be running good and strong.

The problem remaining now is if i set the saw down, it will idle for a bit, and eventually stall out. OR, if i pick it up before it stalls and hit the throttle, it bogs and stalls, simetimes i can get'er to rip if I 'feather' the throttle a bit. For restarting, i can't just start at idle, have to choke first, then it'll start. I attached a recording, maybe that helps explain.

Your recording link doesn't work. It points to some XML file and not an audio file.

These saws were known for fuel pooling in the intake. The tell tale is that if you pick up the saw and/or point the bar tip down a slug of fuel is tossed into the engine which either causes a drop in idle speed or stalls the engine. This can usually be fixed by correct tuning.

 

[stihltech]

Pressure and vacuum test is a must on an 026. Crank seal under flywheel is a common leak.

 

[gary-stihl]

Your recording link doesn't work. It points to some XML file and not an audio file.

These saws were known for fuel pooling in the intake. The tell tale is that if you pick up the saw and/or point the bar tip down a slug of fuel is tossed into the engine which either causes a drop in idle speed or stalls the engine. This can usually be fixed by correct tuning.

Not sure what is up with uploading the MP3.
So, try this link: http://www.stillriver.org/026-problem.mp3

I'll try this experiment.

 

[gary-stihl]

You should also replace the fuel filter as its cheap and removes another potential problem area. Check all the tubes and lines for cracks or leaks with pressurized air.

This could be just a tuning issue, have you set the carb to factory default settings? Do this and then tune from here (plenty of advice online about this). If this doesn't help and you cannot maintain tune, you have something else wrong. I'd move on to checking the cylinder for an air leak.

Yes, the L screw i put all the way into the stop, then backed out one full turn. I have not fussed with it, but sounds like i need to see if moving in/out rectifies the issue

 

[SteveSr]

Not sure what is up with uploading the MP3.
So, try this link: http://www.stillriver.org/026-problem.mp3

I'll try this experiment.

From the sound file, either you are Charles Atlas or that saw has low compression. Surprised that you can get it to run at all. Rings are likely seized due to use of boat oil.

To verify this hypothesis remove the muffler cover and take a small flat blade screwdriver and see if the rings can be moved when you push on them with the screwdriver. Both rings must be free and you should be able to see them move.

Looks like you are in for a rebuild. Do a cleanup and pressure and vacuum test before you remove the jug. This way you won't have to guess at the crank seal integrity.

 

[sean donato]

He checked compression already and came up with 150psi, more then adequate to run. Something else is up. Sounds more like he doesn't have idle speed/ low fuel screw at right.

 

[SteveSr]

He checked compression already and came up with 150psi, more then adequate to run. Something else is up. Sounds more like he doesn't have idle speed/ low fuel screw at right.

Compression could be artificially high due to all of the carbon on the piston and in the combustion chamber.

Also, did you hear all the piston rattle/slap in the audio file?

 

[sean donato]

I listened, but the audio on my phone isn't the greatest.
There would have to be quite a but of carbon to make the compression that high if the rungs are shot. At any rate your pretty much at the tear into it stage.