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

[L34]

Marine oil is for water cooled motors.
Not good for chainsaws.

 

[gary-stihl]

A little cleaner, will work at it a bit more.

 

[gary-stihl]

Ordered new L7T plug (it didn't look too bad), Berryman B12 decarbonizer, and Stihl HP Ultra 2 cycle engine oil. I'll at least douche the exhaust port, use new gas + stihl 2 cyc oil, new plug, and see how she runs before tackling the carb. 50:1 appropriate or do people run 40:1 or something else? I don't wanna turn this into The Great Oil and Mixture Debate #5281812 tho

 

[singinwoodwackr]

Ordered new L7T plug (it didn't look too bad), Berryman B12 decarbonizer, and Stihl HP Ultra 2 cycle engine oil. I'll at least douche the exhaust port, use new gas + stihl 2 cyc oil, new plug, and see how she runs before tackling the carb. 50:1 appropriate or do people run 40:1 or something else? I don't wanna turn this into The Great Oil and Mixture Debate #5281812 tho

Be very carefull scraping carbon out of that port. It can be done without getting pieces into the combustion chamber but it is a slow process.
almost easier to just pull the cyl and do a full clean out and polish, imo.

berryman’s will not dissolve that stuff…has to be scraped out.

 

[JoeMay]

Outboard motor 2 cycle oil labeled TC2 or TC3 should not be used in air cooled 2 cycle engines.

 

[thompsoncustom]

The air filters when new on these saws is poor flowing so clogged can become a issue quick. Also if the choke spring gets weak the choke can be sucked somewhat closed at WOT.

Get that carbon out of the exhaust port without getting it in the cylinder but like said above would probably be easier to take the cylinder off and then you can really polish up the port so it doesn't stick.

You can see a ton of carbon in my ms260 muffler here but with the exhaust port polished up it doesn't seem to stick.

 

[pioneerguy600]

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

Yes, the numbers and letters are on the side of the carb body

 

[stihltech]

The piston is nice and shiny. Which means it is worn out. No machine marks around the piston = worn out. Start there and seals. Of course inspect crank and bearings. Everything else before freshening the insides is money down the drain.

 

[SteveSr]

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?

Screen looks good, almost too good. Engine has been running hot, lean.

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?

NEVER use marine oil intended for water cooled engines in an air cooled 2-stroke. Use a JASO FD rated oil designed for air cooled engines and this doesn't include Stihl Ultra (only FB rated).

 

[SteveSr]

A little cleaner, will work at it a bit more.

Mesh filter. That might explain the worn out piston & rings. Replace it with a manila colored fleece filter.

 

[SteveSr]

Ordered new L7T plug (it didn't look too bad), Berryman B12 decarbonizer, and Stihl HP Ultra 2 cycle engine oil. I'll at least douche the exhaust port, use new gas + stihl 2 cyc oil, new plug, and see how she runs before tackling the carb. 50:1 appropriate or do people run 40:1 or something else? I don't wanna turn this into The Great Oil and Mixture Debate #5281812 tho

What is an L7T plug? That doesn't sound like the right one for that engine. Should be NGK BPMR7A. While you are at it post a photo of the tip of the plug.

 

[gary-stihl]

What is an L7T plug? That doesn't sound like the right one for that engine. Should be NGK BPMR7A. While you are at it post a photo of the tip of the plug.

Here are a few pics. I did not clean it, so what you see is what was operating.

 

[gary-stihl]

Mesh filter. That might explain the worn out piston & rings. Replace it with a manila colored fleece filter.

Any after-market recommendations or go with Stihl and be done with it?

 

[gary-stihl]

This is the oil I have on order: https://www.amazon.com/dp/B005DC0KDC?psc=1&ref=ppx_yo2ov_dt_b_product_details

 

[gary-stihl]

The piston is nice and shiny. Which means it is worn out. No machine marks around the piston = worn out. Start there and seals. Of course inspect crank and bearings. Everything else before freshening the insides is money down the drain.

Is there a how-to video/etc on this you can recommend and also a list of parts I should get? this will be my first go at this, however, i have done a ton of mechanical work on cars as a 'backyard mechanic' for 40 yrs... I'll do nearly any repair, so have reasonable know-how and good tools.

 

[SteveSr]

Here are a few pics. I did not clean it, so what you see is what was operating.

Not been running overly lean but hard to tell from all of the carbon caused by the boat oil.

 

[SteveSr]

Any after-market recommendations or go with Stihl and be done with it?

Stihl. AM air filters are not recommended.

 

[SteveSr]

This is the oil I have on order: https://www.amazon.com/dp/B005DC0KDC?psc=1&ref=ppx_yo2ov_dt_b_product_details

Stihl Ultra is not a great oil. It has been known to cause carbon problems on its own but is not as bad a boat oil. You should be using a JASO FD rated oil (like Red Armor) which may help clean the carbon from the inside of the engine.

 

[SteveSr]

Is there a how-to video/etc on this you can recommend and also a list of parts I should get? this will be my first go at this, however, i have done a ton of mechanical work on cars as a 'backyard mechanic' for 40 yrs... I'll do nearly any repair, so have reasonable know-how and good tools.

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.

 

[gary-stihl]

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/1855050801...bptJ6+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?