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

[gary-stihl]

I would see if you could get a better photo of the piston with a different camera.

If you have a compression tester with a Schrader valve in the tip you might want to take a compression reading. It would be nice if you had a newer 50cc saw in known good condition to compare the reading to. If the compression is low you may also have stuck rings from all of the carbon deposits.

To check seals you need a vacuum and pressure tester like a Mityvac MV-8500 and some home made block-off plates. The MV-8500 can also be used to check your carb inlet needle to see if it is leaking. Ther are plenty of threads on here detailing these procedures.

Let me try a better camera...

 

[gary-stihl]

compression check: 150psi using the one shown in the pic

 

[gary-stihl]

Tried my "good" digital camera. All it wants to do is focus on the two carbonated bolts on either side of the exhaust port.
I did, however, notice "machine marks" (I think) running around the piston, e.g, circling it, not going up and down. I could see it with my eyes, but i'll be damned if i can get a good pic of it. took like 10-15 shots with my good camera, nothing great

 

[gary-stihl]

OK - if you REALLY zoom in on this one, you can see the lines i was talking about above running *around* the cylinder. Not sure if uploading here will diminish / compress the image or not... if it does, then zooming may be hopeless

 

[AlotL1keVegas]

Check the cylinder/piston for scoring on exhaust side. I just took my 026 apart over the weekend. This is what I found. I'm hoping that I'll be able to clean the cylinder up, and get by with a new piston kit.

 

[sean donato]

If your gauge is even half accurate and the pictures you've shown, I doubt there's anything wrong with the top end. Pressure/vsc test, check out all the rubber and fuel lines toss a kit in the carb and go from there.

 

[SteveSr]

Tried my "good" digital camera. All it wants to do is focus on the two carbonated bolts on either side of the exhaust port.
I did, however, notice "machine marks" (I think) running around the piston, e.g, circling it, not going up and down. I could see it with my eyes, but i'll be damned if i can get a good pic of it. took like 10-15 shots with my good camera, nothing great

Some cameras have a way for you to set the focal point of the image. Same with cell phones. On my now ancient Galaxy S8 I just simply touch the screen where I want t he focal point to be.

 

[SteveSr]

OK - if you REALLY zoom in on this one, you can see the lines i was talking about above running *around* the cylinder. Not sure if uploading here will diminish / compress the image or not... if it does, then zooming may be hopeless

Circumferential machining marks are a good sign. They should be least worn directly under the bottom ring.

 

[SteveSr]

compression check: 150psi using the one shown in the pic

Does that gauge have a schrader valve in the tip or just a straight pipe?

150psi is acceptable, however, it may be artificially high if the top of the piston and combustion chamber is caked with carbon.

 

[SteveSr]

Check the cylinder/piston for scoring on exhaust side. I just took my 026 apart over the weekend. This is what I found. I'm hoping that I'll be able to clean the cylinder up, and get by with a new piston kit. View attachment 1088514

Oops! better find out what caused this before you roach another piston.

 

[stihltech]

If there are really machine marks going around the piston, it should be OK. But the question remains why the issue? Back to fuel supply, vacuum and pressure test. As far as compression, I never use a gauge, as internal condition is THE most important an a 2 stroke. The seal behind the flywheel is very common as is all rubber hoses and intake manifold as stated by many. Also bearing cages are suspect. It is an old saw. Age will be a factor.
The throttle linkage also wears and loses the fast idle. I little bend to make it longer makes a big difference on a cold start.

 

[SteveSr]

air filter... struggling to find the right one there are sooooo many aftermarket. I think original part is

1121-120-1617​

which is that mesh filter.
Is this

1121-120-1618​

the replacement with felt filter?

eg, this guy: https://www.ebay.com/itm/185505080112?hash=item2b30f6e330:g:liQAAOSwvXBiXjxh&amdata=enc:AQAIAAAA8KauEbzxPHrKsMgofedMUgSVUHwiIp42RpvQ7sQQoqgi3leDeFDkI9/eIn4XE5WVxAw4aYkypvsaj77uGZ+P5UFKnLcnuiETqDDb6JGb0nuDCGbwnJz0LztopXoTrjJNW5a9TOjiToA0Mpd2YRKcGAuTtAUZHLpnFhFPfJ2X146Df0Js1qpggJoqimuMO2Qv0J63y9IB9q/QqvX3z1yH4C7Vq2NiWzDfLDzotpurF0X6YaEEqc+MUynt9qAq4pj8y/y7NN9kddRPSHwiqjVCqnJlLQxZQgJmcO3TTOmFnibptJ6+A+Y2ukk63pnd71fZXA==|tkp:Bk9SR9zm2beSYg

visually, looks same as mine. I notice some do not have the extra hole to fit over the carb.

also, where do you guys get parts online? any "go to" places?

1618 is the filter that you want for the compensating carb. The Ebay listing looks to be genuine. You can also check for the Stihl part numbers and logo molded into the plastics.

 

[AlotL1keVegas]

Oops! better find out what caused this before you roach another piston.

It's going to get a rebuild. It will get a top end, crank bearings, and crank seals. All OEM parts of course. I'm just hoping the cylinder isn't rocked, and it just needs a piston/rings.

 

[gary-stihl]

Does that gauge have a schrader valve in the tip or just a straight pipe?

150psi is acceptable, however, it may be artificially high if the top of the piston and combustion chamber is caked with carbon.

schrader valve. i put the saw in a vice by the bar, with one hand, held the gauge in tight to the spark plug hole, and the other do several rapid pulls.... and watch the gauge.

 

[gary-stihl]

It's going to get a rebuild. It will get a top end, crank bearings, and crank seals. All OEM parts of course. I'm just hoping the cylinder isn't rocked, and it just needs a piston/rings.

Mine does not look ANYTHING like that one! YIKES. Also, looks like you have a crack below the exhaust port or is that just crap that looks like a crack?!

 

[gary-stihl]

Some cameras have a way for you to set the focal point of the image. Same with cell phones. On my now ancient Galaxy S8 I just simply touch the screen where I want t he focal point to be.

Yep, aware of that, and I just could not get the iphone 13 mini to cooperate. because the phone is soooo compact, they ditch the micro/closeup lens, as i cannot take anything super close up. Oh well....

 

[gary-stihl]

If your gauge is even half accurate and the pictures you've shown, I doubt there's anything wrong with the top end. Pressure/vsc test, check out all the rubber and fuel lines toss a kit in the carb and go from there.

yah, i think that is the approach I shall take. Plus fresh 93 oct gas with the Stihl HD oil (next time will get the stuff SteveSr mentioned) and we'll see if she rips or needs more investigation & love

my 036 cuts like crazy; but it too prob needs a tune up

 

[gary-stihl]

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.

 

[sean donato]

It should take a k20-wat walbro kit. Just like all the wt series. It's not a stihl item.

 

[gary-stihl]

It should take a k20-wat walbro kit. Just like all the wt series. It's not a stihl item.

ordered. thanks mate.