Stihl 026 rebuild

[drf255]

Not sure.

The opening (didnt measure internal venturi) is the same on the 394 and the 403 (?-the 260 carb) as the 194.

The needles are differently spaced on the 403 carb though, so the holes in the case may not match.

I havent tried them back to back on the same saw.

 

[Macman125]

I am pretty sure it has the largest venturi size of any that came on the 260. It also has an adjustable high side. I have the 22 on mine which is still fully adjustable but not quite as performance oriented as the 194.

 

[Brewz]

Makes sense
I have tracked one down and going to get it. Can't hurt to try it

 

[Brewz]

What a day
Everything I need for the rebuild showed up at once!
So it begins.

 

[gritz]

As far as the carbs, they are all very similar in venturi size. I think I listed the sizes of a few of the different ones in my frankensaw thread. I'll look to see if I can dig that up somewhere. If not, I probably have one of just about every carb that came on those things. I might have to see about doing a performance test on the ported saw, but I anticipate no real difference in performance between the 194 or 394. Maybe the 22B because it's venturi is much smaller if I remember right.

Edit: The info on the carbs is on page 2 of my 024/026 Frankensaw thread.

http://www.arboristsite.com/community/threads/024-026-frankensaw-project.214108/page-2

 

[Brewz]

It's alive........ IT'S ALIVE!

 

[Brewz]

Bolted it all back together, made a new thin gasket and got a .009 squish with the new Meteor piston.
When I used the original factory gasket I got .018, so I left it in there. I will order a new one and replace it but it was still perfect so was happy to bolt it on.

I checked the timing again and got 95* exhaust and 117* on the transfers.

Everything went back together really well.
I discovered it didn't have any chain bumpers on the saw frame or the sprocket cover. I had 3 spare ones but will have to order more.
Fitted new springs to the clutch and have saved the carb rebuild kit for the WT-194 when it shows up.

My compression tester has something wrong with it and is reading about 30 - 35 psi low on all my saws. It measured 155psi which I am calling 185 psi fresh before starting.

Fueled it up and added a dribble extra oil for the first tank.
Pulled the cord 3 times and it kicked, clicked off the choke and pulled the cord again and it fired up...... rough, but running. Idle was really low and it kept stalling out.
Tuned the LA and L screws to get a good idle and it runs great.
Haven't tuned the top end yet as its raining real hard and is flooding and am busy re-directing water, but it winds up FAST and smooth. I will give it a go tomorrow and see what sort of RPM she makes.

 

[drf255]

 

[Brewz]

The other thing I noticed was it had no chain catcher.
I asked the guy running the local Stihl shop if he could order me the bits.
He looked through his parts schematics and told me they dont have one.

I thought...... OK..... a pro saw with no chain catcher?

I found the parts and numbers in my parts PDF and will go get them ordered tomorrow. I wont be cutting any wood with it without a chain catcher!

 

[drf255]

It's simple to make. A piece of 1/8 aluminum. Follow the pattern on the plastic AV mount. Leave a tab and bend it up.


Won't take long.

 

[drf255]

Sent from my iPad using Tapatalk

 

[Brewz]

Thanks for the photos mate, but mine does not even have the white plastic mount.
I need the mount, screw and chain catcher.

 

[Terry Syd]

Brewz, you had some success using the modded 460 carb on your 039. If you want to try a similar 'low speed circuit' mod on your 026 it can be done. One way is drilling the air bleed holes, the other is using a much stronger metering spring.

If you post the pictures of the inside of your carbs, in particular the metering springs, perhaps we can get a bit more torque out of the 026.

As I recall the WT will take Zama springs. I have a selection of them and could send you a couple of fairly stiff ones to try.

Here's a good way to test to see if extra fuel in the low speed circuit helps - just open it up more and see if the saw has more torque down low (tune for the same WOT with the high speed needle). It may be pig rich at idle and bog a bit on acceleration, but you want to test it in the wood while cutting. You'll probably have to screw in the idle adjustment just to keep it idling (rough as it may be)

If it does have more torque, then you can probably clean up the idle and acceleration with a stiffer spring.

 

[Brewz]

Ok.
Went and ordered the chain catcher parts this morning.

I ran it back up and opened it right up. got 10400 rpm and lots of smoke.
leaned it out to full lean and then brought it back to where it started to roughen up which was about 13700 rpm.

I then pulled the carb apart to take some photos which are below.
I dug through an ice cream container full of random "bits and pieces" and found a bag with all the bits from when I rebuilt the 039's carb. The spring is identical in size but about 50% stiffer. Its the one on the right in the picture.
Looking at the jet holes for the H and L, they look big enough to supply fuel so I went with the easily reversible spring option.

Fitted the stiffer spring and replaced the needle with a new one, and bolted it back on.
Pulled the cord a few times and it wouldn't fire up. tried a dozen times and nothing. It flatly refused to go.
So I started back in to change the spring back and found I had left the throttle linkage out
I had a laugh at myself and fitted it back in.
Fired it up and it was idling 500 rpm lower. It needed the LA screw increased a bit and then richened out the L screw. This resulted in a richer top end which needed the H circuit leaned out a touch to get the revs back up again.

So it sounds like the saw is now sucking more fuel via the L circuit which was the desired result, and should give good torque in the cut. Throttle response is still really good. I am sure I will do some fine tuning when I get to use it in some wood and the rings run into the cylinder a bit better.

I'm not going to test it in timber till I get a chain catcher fitted and I won't be able to get to any wood to cut for a few weeks now as we have had a foot of rain in the last 2 days and its flooding.

What I need is someones gum tree to fall over across the road somewhere local so I can go help out the emergency services and test my saw at the same time

Edit: forgot the photos

 

[Brewz]

I would love to see some pictures of the inside of a WT-194 to compare jets and spring to the WT-394 above

 

[Terry Syd]

Brewz, you're picking up on this carb tuning real quick. Yeah, that 039 spring is a lot stronger - thicker wire, longer spring and more pitch to the winding. No doubt you could feel it as about 50% stronger when you compressed it.

Here's something else to consider, the size of the metering orifice under the valve. The smaller the orifice the longer the 'ramp' of the fuel to full open. In other words, you can lean out the throttle response with a smaller orifice.

It would be interesting to see the size of the metering orifice between the 194 and 394. - Like you said, it would also be interesting to see the difference in springs between the two carbs.

The difference in the carbs could be a slightly different drilling of the air bleed holes, but you may have to pull the Welch plugs and push some micro drills through the holes to check them.

My gut feeling is that I think you may be able to tune the carb sufficiently with just tweaking the springs. If you want to get more fuel out of the low speed circuit, you could just shim that 039 spring with a washer or two.

 

[Brewz]

I will have my very own 194 soon and will definitely be doing some comparison measurements.

I am pretty happy with the throttle response and will wait till I get it into some timber to play with it some more

 

[Macman125]

What would be considered an acceptable squish on these saws?

 

[Brewz]

I just pulled my compression tester apart and checked the gauge against the gauge on my compressor.
It reads the same.

I am concerned that I am only getting 155 psi with the new piston and rings when I got 175 before I stripped it.

What might cause this drop in compression?

 

[Brewz]

What would be considered an acceptable squish on these saws?

about 018 to 020 from what I have read