Weird Problem with Stihl 026

[max2cam]

Older 1990s vintage 026. Normally a good, strong runner. Runs non-ethanol gas with Stabil. Did sit for a few weeks.

Saw will NOT start cold. Sparkplug looks dry. Fuel filter passes gas -- at least I can blow through it. Saw starts right up if I put gas down sparkplug hole or in carb. Then it runs fine. Restarts right up when hot. But if it sits overnight it won't start again unless I put gas down sparkplug hole. Obviously it does not seem to be getting gas when I pull it cold but does get gas once it gets running and when hot.

Before throwing parts at it or soaking the carb in PineSol again (worked once before), I thought I'd get some advice from you guys who are smarter than me about these saws. Any other time I had to pour gas directly into the cylinder to start any small engine, it would thereafter start and work fine. Not this time. Thoughts on the cause of this 026 weirdness? Thanks!

 

[82F100SWB]

Do you have an OEM or aftermarket air filter on there? I have came across aftermarket filters that the choke didn't close properly.
Could be a carb issue as well.

 

[capetrees]

fuel line cracked?

 

[NCPT]

I have came across aftermarket filters that the choke didn't close properly.

This was my problem with my 026 that was tough to start cold.

 

[capetrees]

compression problems?

guessing

 

[Patrick62]

fuel diaphragm in carb is most suspect.
impulse line is good or it would not stay running. While got carb apart, check or replace the metering diaphram.
non-ethanol fuel helps, but there are a few other things in there that cause some problems eventually

 

[Tom B.]

I like the idea of the choke not working properly. We know it's getting fuel when running or still warm, but seems to be lacking fuel when in full choke.
Why?
Could something else in the fuel system open up a bit when it's warm or running that closes itself off when cold? Thermal dynamics causing this?

 

[max2cam]

Guys,

Has newish OEM air cleaner ($25). Even so, I just checked and choke is closing.

Compression seems very good.

Diaphragm in carb has been in there for at least 3-4 years. Don't recall for sure if I replaced it when I soaked carb in PineSol when it was clogged up. Don't think so because it recently had a carb rebuild just before I got it which had not fixed a poor running issue, but the PineSol soak did.

I'll put new diaphragm #1 on list.

I also adjusted the carb a while back. But it idles good now when its running. Which screw controls the starting mixture? Idle or Low Speed? Maybe I should open the low speed jet a bit and see if that helps? Could carb be out of spec, not start cold, but still run and idle okay and restart hot? Seems unlikely, but????

Summary: it's not drawing gas on cold startup, but starts/runs normal after adding gas and also restarts hot. Could a bad diaphragm work better hot & fail to work when dead cold? The diaphragm and rubber lines were replaced with OEM parts before I got it 3-4 years ago. They aren't ancient, yet something isn't right.

Thanks!

 

[windthrown]

Which carb do you have on it? They came with at least a dozen different ones. Walbro WT-194 was the best one of the lot. I would blow out the carb. Sounds like a tiny piece of crap is in the L jet to me. Or t is not adjusted right. Try seating the L and H screws and resetting them to the default. Then use a tach to re-set the low and high side (method is below). Also check the fuel line, and make sure it is not leaking. They tend to hairline crack over time in any Stihl saw. And check that the tank vent is working. It can get clogged and keep the fuel pump from sucking up gas. There are several tank vents on the 026/260 line of saws. Also check the impulse line. Same issue as the fuel line. If that has a slight leak, it will not draw enough gas. Or just enough to run when warm, but not when cold. And did you check the fuel filter? Same issue on all these with not getting gas when cold.

Both the idle LA and L screw control the low speed mix and revs. To set the L and H to the default positions, which is to set them each one turn out from bottom. Start the saw and let it warm up. Then with the tach raise the idle to 3600. Then turn the L screw in or out to get the max revs, then reset the idle to 3600 again and re-adjust the L to get the max revs, and repeat until you get the max revs of 3600 with the L screw. Then lower the revs to 3300 with the idle screw, and further lower the revs to 2800 with the L screw. That is the method for tuning the low side from the 260 service manual. Once that is set, you can adjust the H side to a max of 14000 (the real red line is about 15000). I set the H screw to 14000 RPM and run it WOT out of the wood and adjust it until it burples (4-strokes or whatever you want to call it). Then run it WOT in some wood. The sound should clean up and the burple goes away in the wood. If not lean the H screw out a bit and try again. If the sound is clean out of the wood fatten it up by opening the H screw a tad. If in doubt, let it burple a tad when WOT in the wood, that will be slightly rich. You want to err on the rich side. Running lean can do damage. If the saw is over 15k at WOT, I fatten up the H mix (open it up) to drop the max revs.

 

[NCPT]

.

 

[president]

fuel diaphragm in carb is most suspect.
impulse line is good or it would not stay running. While got carb apart, check or replace the metering diaphram.
non-ethanol fuel helps, but there are a few other things in there that cause some problems eventually

T1

 

[SEAM]

The choke is easy to check.
- remove air cleaner housing cover
- engage choke
- hook your fingernail under the little white choke lever of the filter - if it can moved up/down a little the actuator on the switch shaft is worn/bent/too short.

In cases like this I usually just stick a piece of fuel line on the actuator and cut it the right length

 

[max2cam]

Update to OP. I know this is old but for the record the weird no-start-when-cold problem was caused by a gummed up screen inside the carburetor. I noticed it right away when the carb was apart. Funny, because everything else was perfectly clean. But I sprayed and blew out the passages and rebuilt the carb and now it's running again. Beware the clogged screen! It'll make your saw run erratically and cause hard starting problems too.