Stihl 026 - carburetor and/or crankcase leak

[nedsim]

I've been looking for something a bit larger than my old reliable 024 and came across a great deal on an 026. It wasn't running but is in great shape -- clean, nothing missing or broken, piston is clean with no scoring. $100 and 15 minutes away. A no-brainer. The seller said the last time he used it, it started right up, then died. He had replaced the carb several years before.

What I found:
The carb was way out of adjustment. In particular, the low jet was backed out 3 turns or more.
The spring in the air filter that holds the choke butterfly open was unhooked.

What I did:
Drained the fuel and replaced it with fresh canned fuel.
Fixed the choke spring.
Set the jets open 1 turn each.
Checked the spark -- OK.

Still wouldn't start.

A squirt of mix in the the carb and it started on the 1st pull, but wouldn't continue to run.

Pulled the carb, which looks like new, but is presumably Chinese. No markings of any kind on it. Opened it up and pulled the needles and cleaned out the passages as best I could. Put it back together and it starts and runs.

But...and here's the question: The tuning doesn't seem right. The idle adjustment needs to be bottomed out to get an idle and only if the low needle is closed a bit more than the point that gives good throttle response. Thinking maybe it was just the way the adjusting screw is mounted, I compared the butterfly position of the properly adjusted 024 to the position of the 026 -- the 026 is open much more than the 024 at idle.

The saw runs strong -- I've been testing on a 16" oak that we cut down recently. The saw has 16" bar and .325 chain. Even without a side-by-side comparison, it clearly has more oomph than the 024, with the same bar & chain.

It also seems to use more fuel than I'd expect.

My first thought was a vacuum leak, but I'm also suspicious of the carb itself. Any advice before I make up the parts to do a vac/pressure test?

 

[irhunter]

I don't follow your description of the carb adjust. So, you snug the 2 screws down clockwise...how many turns counterclockwise are you on the L and H screws?

 

[ballisticdoughnut]

Do the pressure/vac test. If it passes great if not fix whatever is wrong and get a genuine walbro carb. Chicom parts are garbage.

 

[nedsim]

I don't follow your description of the carb adjust. So, you snug the 2 screws down clockwise...how many turns counterclockwise are you on the L and H screws?

I started at 1 turn CCW. Ended up at about 1-1/2 turns CCW for both. What threw me was the fact that the saw won't idle unless the idle screw is turned in (CW) all the way, and then just barely idles. If I lean the Lo to bring up the idle, then the saw is sluggish accelerating.

 

[nedsim]

Do the pressure/vac test. If it passes great if not fix whatever is wrong and get a genuine walbro carb. Chicom parts are garbage.

Thanks, mostly looking for a sanity check here. In other words, am I missing something obvious?

Re a new carb, I see Walbro WT-194 carbs advertised as replacements for the 026. Is that correct?

 

[irhunter]

Thanks, mostly looking for a sanity check here. In other words, am I missing something obvious?

Re a new carb, I see Walbro WT-194 carbs advertised as replacements for the 026. Is that correct?

I think you're fine. A pressure/vac test on a new-to-you saw is never a bad move. Same goes for checking max RPM with a tach.

Yes, the WT194 is a good choice...if you buy from a source you are sure isn't selling knock-offs.

But, I am not sure you have a problem with the carb you've got. Many people run AM carbs and are happy with them.

The 026 should pull better, and use more fuel, than the 024. If there is a really big difference in how the 026 pulls, your 024 might need looking at. Maybe low compression?

 

[wildwes]

Cracks in fuel lines and impulse lines can cause all kinds of grief. Just because the guy you bought it from changed the carb doesn't mean that he changed the lines. I also put a brand new OEM line on a MS260 a month or so ago and couldn't get it to tune right, looked in the tank and the brand new line had split. Aftermarket lines can be too long and kink between the carb and the tank.
Fuel lines are my first stop on these saws if there are running issues.

Chinese carbs can give some problems too, or run great- they are pretty much a crap shoot. Personally, I would rather have one WT-194 than a dozen chicom carbs if offered the choice.

 

[pioneerguy600]

From what I can glean from the OP`s posts the saw adjustments have been leaning toward giving the engine more air, not less so it does not sound like there is an air leak but its getting too much fuel at idle. Adjusting in the idle adjustment screw gives the engine more air and so does leaning out the L screw. The H may be a bit too rich or the carb is not flowing the correct fuel mix through the throat jets into the air stream of the venturi.

 

[Bob Hedgecutter]

I started at 1 turn CCW. Ended up at about 1-1/2 turns CCW for both. What threw me was the fact that the saw won't idle unless the idle screw is turned in (CW) all the way, and then just barely idles. If I lean the Lo to bring up the idle, then the saw is sluggish accelerating.

And this is the lottery of AM carbs.
You are probably lucky the H and L circuits are behaving normally at 1 1/2 turns ccw and holding tune- this is acceptable.
Really, if H and L stay there, it is the idle screw that is giving you bother and you need to see it the tab on the throttle plate can be adjusted out to contact the backed off screw more towards the point of the screw taper. The action of the screw being wound in needs the taper to be in full contact with the throttle plate from the get go.
Personally I had issues with an old 024S that came to me with original carb- but the threads in the alloy arm in the carb body that the idle screw work in were flogged out and loose- as the engine ran, the idle screw would back out- I re tapped that to 5mm and ground a T27 screw to fit.
Bestest fix for you- find an original or genuine replacement carb.

 

[nedsim]

Thanks to everyone. Sounds like the sensible thing is to run a vac and pressure test and apply the mentioned tuning tips before blaming the carb. If I was depending on this saw to run every day I'd be ordering a Walbro and OEM fuel & impulse lines and be done with it. It may come to that just to set my mind at ease, but I have the time to mess with it.

 

[ZeroJunk]

Adjust your carb to get the response you want and don't worry about how many turns it is or isn't.
It is not uncommon for some of these saws to reach peak idle all the way in, but they may not make a transition from idle. So, turn it out 3/4 or 1 and adjust the idle speed adjustment so it will stay running but slow enough the chain does not continue to turn. You have to have enough fuel at idle so when you open the butterfly wide open it does not starve.

 

[nedsim]

I'll fuss with the carb and linkage (per Bob Hedgecutter) some more 'til I get to running the leak tests. Thanks.

 

[Patrick1903]

I'll fuss with the carb and linkage (per Bob Hedgecutter) some more 'til I get to running the leak tests. Thanks.

@nedsim How’s the saw running? Was throttle plate not in good contact with idle screw? Did you ever vac and press test? I have a similar saw and need to vac and pressure test. Was just perusing threads on 026 and 260.

 

[HumBurner]

@nedsim How’s the saw running? Was throttle plate not in good contact with idle screw? Did you ever vac and press test? I have a similar saw and need to vac and pressure test. Was just perusing threads on 026 and 260.

Thanks for bumping. I also experienced this recently with an 024 and haven't had time to check it over.

 

[nedsim]

@nedsim How’s the saw running? Was throttle plate not in good contact with idle screw? Did you ever vac and press test? I have a similar saw and need to vac and pressure test. Was just perusing threads on 026 and 260.

I'd been waiting 'til I have more experience with the saw to follow up, but... We had a break in the weather and I went out a couple weeks ago to do some cleanup of stuff that's fallen over the winter. The saw wouldn't start after sitting for 6 weeks or so on the shelf in the unheated shed right next to my 024, both fully fueled the way I always store my saws. I've never had any trouble doing this as long as I start them every couple months and keep the fuel reasonably fresh.

Since the symptoms were exactly the same as when I got the saw, and what the original owner had experienced, I didn't bother cleaning the aftermarket carb again and replaced it with a Walbro WT-194 -- the saw started right up and idled fine with the throttle plate in what appears to be a more typical position. The weather has turned again, so I haven't had a chance to tune it while cutting yet. I think the true test will be what happens after the next time it sits for a month or two.

I did pressure and vac test the saw back in January, and it was fine. I have not replaced the fuel and impulse lines as I saw there may be some confusion over getting the proper OEM parts and I didn't want to find I had ruined good parts in removing them without having the correct replacements on hand. I've gotten quite proficient at replacing the carb now that I'm familiar with the trigger and throttle linkage. About 15-20 minutes from start to finish.

 

[Patrick1903]

I'd been waiting 'til I have more experience with the saw to follow up, but... We had a break in the weather and I went out a couple weeks ago to do some cleanup of stuff that's fallen over the winter. The saw wouldn't start after sitting for 6 weeks or so on the shelf in the unheated shed right next to my 024, both fully fueled the way I always store my saws. I've never had any trouble doing this as long as I start them every couple months and keep the fuel reasonably fresh.

Since the symptoms were exactly the same as when I got the saw, and what the original owner had experienced, I didn't bother cleaning the aftermarket carb again and replaced it with a Walbro WT-194 -- the saw started right up and idled fine with the throttle plate in what appears to be a more typical position. The weather has turned again, so I haven't had a chance to tune it while cutting yet. I think the true test will be what happens after the next time it sits for a month or two.

I did pressure and vac test the saw back in January, and it was fine. I have not replaced the fuel and impulse lines as I saw there may be some confusion over getting the proper OEM parts and I didn't want to find I had ruined good parts in removing them without having the correct replacements on hand. I've gotten quite proficient at replacing the carb now that I'm familiar with the trigger and throttle linkage. About 15-20 minutes from start to finish.

Glad to hear you’ve had good success with the new carb. Did you tune the carb, and are you getting a 4 stroke burble when unloaded at WOT, then cleans up in the cut? Just make sure you’re rich enough with the new carb. I replaced a carb a couple years ago with a non oem and the saw was screaming until I opened up the high side.

 

[nedsim]

Glad to hear you’ve had good success with the new carb. Did you tune the carb, and are you getting a 4 stroke burble when unloaded at WOT, then cleans up in the cut? Just make sure you’re rich enough with the new carb. I replaced a carb a couple years ago with a non oem and the saw was screaming until I opened up the high side.

I haven't had a chance to tune it under load. All our snow for the winter has fallen in the last couple weeks, at least it feels that way, so anything big enough for a real test is buried now. Got it running with just an initial 1-1/2 turns out on both H & L and the idle is pretty close right out of the box. Throttle response is good. It's running very rich to my ear and I'll leave it that way 'til I can run it under load.