Stihl 026 rebuild

[drf255]

It's gonna take a few tanks for the compression to jump. The rings have to seat.

I'm lost on your carb mods. Wouldn't a stiffer metering spring lean you put on the HIGH side? Is that what you want because you are richen in the idle circuit?

I've built around 5-6 pretty hot 026's at this point. Some pulling 240psi and spinning 16,000 rpm+. I've never done a single thing to the 194 carb short of raising the metering lever a bit higher than the Walbo setting to richen the H side a bit.

Try the saw with and without the air filter. The flocked air filters in these saws suck ass. I recently had one that wouldn't run at all with a brand new one. Drove me nuts. 2 spark plugs and 3 Carburetor's later, I tried to start it without the air filter and it came to life. You need the metal filter for any real perfomance mods.

 

[Brewz]

I'm lost on your carb mods. Wouldn't a stiffer metering spring lean you put on the HIGH side? Is that what you want because you are richen in the idle circuit?

The idea is to supply more fuel via the LOW circuit increase torque when the saw speed drops under a lot of load.
With the stiffer spring, I actually had to lean out the HIGH side as the LOW was supplying more fuel.
The way I see it is that it doesn't matter where the fuel comes from at WOT, as long as there is plenty of fuel when the engine speed drops under load. If your LOW circuit is set very lean to give better throttle response, it wont supply enough fuel at higher revs.
I'm not really sure what the ratio's are for H and L fuel delivery at what rpm's but it sure worked on my 039 with a larger carb that pumped in more fuel on the LOW circuit.

Try the saw with and without the air filter. The flocked air filters in these saws suck ass. I recently had one that wouldn't run at all with a brand new one. Drove me nuts. 2 spark plugs and 3 Carburetor's later, I tried to start it without the air filter and it came to life. You need the metal filter for any real perfomance mods.

It came with a Stihl flocked filter and when I try and blow through the flock surface its very restrictive.
I bought one of the cheap Chinese jobs with the white fine mesh material and it flows WAY better. I had to pull it apart and trip up some plastic casting lips so the choke flap would open back up after closed but other than that its great!
I have one on my 039 as well and works well.

 

[drf255]

The idea is to supply more fuel via the LOW circuit increase torque when the saw speed drops under a lot of load.
With the stiffer spring, I actually had to lean out the HIGH side as the LOW was supplying more fuel.
The way I see it is that it doesn't matter where the fuel comes from at WOT, as long as there is plenty of fuel when the engine speed drops under load. If your LOW circuit is set very lean to give better throttle response, it wont supply enough fuel at higher revs.
I'm not really sure what the ratio's are for H and L fuel delivery at what rpm's but it sure worked on my 039 with a larger carb that pumped in more fuel on the LOW circuit.




It came with a Stihl flocked filter and when I try and blow through the flock surface its very restrictive.
I bought one of the cheap Chinese jobs with the white fine mesh material and it flows WAY better. I had to pull it apart and trip up some plastic casting lips so the choke flap would open back up after closed but other than that its great!
I have one on my 039 as well and works well.

Ahh,

So your saw is wearing an MS260 rear cover and AF. They flow OK, but not like metal. Give it a quick blast with no AF and check the tach.

As for the carb, I'd love to hear more on your theories on this. I set my carbs to the highest idle rpm, then richen until throttle bOg goes away. As for the H side, I set it so it just doesn't 4 stroke in the cut at intended bar pressures. I can get it overly rich easily that way. It's just richer when piss revving, but who cares.

I finally tached my last 026 while cutting. With a 104 exhaust and a stock 194, I'm at 11,000 rpm with a 16" .325 bar buried in hardwood. That's with a decent amount of down pressure too.

My point here is that my carb is just fine with no mods. I'm not sure why yours isn't.

 

[drf255]

This is the last one I built with a 16" bar noodling maple.

Totally stock 194 carb with metal filter.

Does it sound lean?

 

[Brewz]

Never questioned your work mate.......... woo back there.
Your work is an inspiration!

I am just playing and learning and do plan to try the saw with both springs.
There was nothing wrong with the carb, I was interested to see if it would work with either spring and it did. It works very differently with the different springs and this is what interests me.
When I get to use it in some wood, the plan is to run it bar deep in some hardwood and see how it goes when I lean on it. Then change the spring out, tune and try again.

Where do I get a metal filter and how do they go with dust?

 

[drf255]

Never questioned your work mate.......... woo back there.
Your work is an inspiration!

I am just playing and learning and do plan to try the saw with both springs.
There was nothing wrong with the carb, I was interested to see if it would work with either spring and it did. It works very differently with the different springs and this is what interests me.
When I get to use it in some wood, the plan is to run it bar deep in some hardwood and see how it goes when I lean on it. Then change the spring out, tune and try again.

Where do I get a metal filter and how do they go with dust?

I wasn't insulted and wasn't trying to insult you.

You guys know more about carbs than I do.

I'm simply pointing out that you can make a strong runner with a stock carb. In fact, I worry that your mods may actually make the saw run worse.

Try your saw with no AF before you look for metal. It may not need it.

 

[Brewz]

The plan is to test the carb stock and with the stiff metering spring to see if it feels any different.

Will try it without the air filter but I am impressed with how well the after market filter flows

 

[Macman125]

I have to get a new case. This thread has me itching to start on mine.

 

[dall]

yes i need to start on another of mine also i have 4 or 5 in waiting lol

 

[Terry Syd]

I'm lost on your carb mods. Wouldn't a stiffer metering spring lean you put on the HIGH side? Is that what you want because you are richen in the idle circuit?

There are two fuel curves in the carb, the straight section with the low speed circuit has one curve and the high speed circuit with the venturi has another. We are blending the two fuel curves to get a more even fuel mixture for the air flow that is going through the carb at different RPMs. Many of the EPA carbs have been set up for a lean low speed circuit to reduce emissions. We're 'fixing' that...

I'll get a link to a thread that has heaps on diaphragm carb tuning. It took me months to figure out this stuff...

Here it is - http://www.arboristsite.com/community/threads/dolmar-7900-carb-upgrade.229528/page-2

There is also a link in the thread to another thread about a 'Chinese carburettor'. I went through some other carb issues in that thread.

 

[Macman125]

Came across a thread on making these to eliminate the pesky tiny little band at the very edge of the cylinder, it works great!

 

[Brewz]

Yes that little band is a pest.
I can't think for the life of me why it's even there.

I am thinking about taking mine to amate with a laythe to have it removed and get a proper squish

 

[drf255]

That band IS the squish band and the entire chamber is domed/hemispherical beyond it. Even the band is at an angle/arc. You shouldn't remove it unless you intend on cutting the entire chamber and piston flat.

 

[drf255]

There are two fuel curves in the carb, the straight section with the low speed circuit has one curve and the high speed circuit with the venturi has another. We are blending the two fuel curves to get a more even fuel mixture for the air flow that is going through the carb at different RPMs. Many of the EPA carbs have been set up for a lean low speed circuit to reduce emissions. We're 'fixing' that...

I'll get a link to a thread that has heaps on diaphragm carb tuning. It took me months to figure out this stuff...

Here it is - http://www.arboristsite.com/community/threads/dolmar-7900-carb-upgrade.229528/page-2

There is also a link in the thread to another thread about a 'Chinese carburettor'. I went through some other carb issues in that thread.

Interesting stuff. Thank you.

I have to read the entire thread.

I'd be interested to see what the OP's 026 does with mods to the carb.

 

[Brewz]

And tested it shall be!

 

[bikemike]

How much did you spend on piston and rings OEM or aftermarket?

 

[Macman125]

That band IS the squish band and the entire chamber is domed/hemispherical beyond it. Even the band is at an angle/arc. You shouldn't remove it unless you intend on cutting the entire chamber and piston flat.

The cyl pic is not very revealing. I didn't get into the tapered part of the combustion chamber at all. With this tool, I stuck the cyl in my bench vise, inserted the piston with the modified piece of file, manually spun it and cut the squish till it was flush with the start of the taper. It worked quite well surprisingly.

 

[Stihlofadeal64]

meh, modded saws -- does anyone even do that anymore

 

[Terry Syd]

I have to read the entire thread.

I should have mentioned that Rich was working on a Zama carb which has entirely different circuits to the Walbro. In the Zama the idle mixture screw ONLY affects the idle mixture. The low speed fuel flow is controlled by the jets he drilled.

On the Walbro the low speed needle affects the idle mixture AND the low speed circuit flow.

You want to check the air bleed/transition holes and see if one or both are BIGGER than the other carb. If they are bigger, they will LEAN out the idle and allow you to add more fuel to flow through the low speed circuit.

The size of the metering orifice will also affect the 'ramp' of the fuel flow off of idle. The SMALLER the metering orifice, the longer (and leaner) the fuel delivery will become. Which will allow you to open up the low speed needle even more.

 

[CR888]

Last weekend I brought home from my local tip two ryobi lawn hornet trimmers. Not that anyone needs a lawn hornet, I figured with two units I could make a cheap runner and have some spare parts at hand. Well fuel lines crumbled when touched and carb diaphragms were similar to crocodile skin. Both carbs needed rebuild kits, they ran but poorly. Being I did not want to wait for parts and tip money into these crappy things, I used another larger venturi carb off a blower and with some mods, made it fit and work (despite having to now remove muffler or carb to access h/l screws). Well WOWZERS this trimmer now runs much harder than it did. A little hard to start, but when running it has much more torque. This was just a learning practice but it told me how much power can be had from different fuel delivery. l like threads like this that get into the nitty gritty of carbs, porting is only one piece of the puzzle and carbs are definitely worth looking at when seeking more power. I just ordered a walbro metering spring kit for $59, junk carbs now get kept or stripped of parts. It's kinda addictive now and every thing I run I think how it could improve with attention paid to its carb. Until now I have been reluctant to use my micro drills on expensive saws with pricey carbs but having a few junk runners to play with will help improve my skills and confidence.