026 Carb's

[Brewz]

Howdy folks

I started a thread on the rebuild of my 026 over on "that other forum" and am a tad sad at the loss of the several pages of pictures and information.

Before I get into the carbs, I will post up a few pics of the saw.

026 Pro, original OEM jug that got a mild porting with widened intake and exhaust, polished exhaust port and raised transfers, Meteor piston, MS260 nylon air filter, port matched modded muffler..... yada yada yada.

 

[Brewz]

 

[Brewz]

Now the carbs.

The saw came setup with an MS260 air filter and a WT-394 carb.
Everyone seems to bolt on a WT-194 carb if they are building the saw up for more performance so I thought I would get one and check it out.

This morning I removed the WT-394 from the saw and rebuilt the WT194 with fresh gaskets etc.
I also wanted to see if there was any real difference between the older and newer carb.

First up I wanted to check out the metering springs.
I had the spring from each carb and the one that cane with the kit. All 3 were different.

Left: WT-194
Middle: WT-394
Right: Overhaul kit spring

The 194 spring was stiffer than the 394's spring. The Kit spring was sort of in between.
I rebuilt the carb and left the original heavier spring in the carb.
I shouldn't say "original" spring because I may well have been re-built before.



The L and H fuel jet holes look to be identical in both carbs
Left: 194
Right: 394



Metering hole looks the same too



They are identical up the guts too



I fitted the WT-194 up to the saw and tuned it up.
I am thinking the main difference is the metering spring tension

Plan is to take it out and get it fine tuned in some timber, then swap the metering spring to the lighter spring that came out of the 394 and see what difference it makes to the tune.

 

[Brewz]

While I had it apart I tidied up the screw holding the butterfly

 

[Brewz]

With the popularity of these little saws and the amount of people putting a lot of work into them, I thought a thread based around the carbs would be a good idea.

I would love for people to post up their carb experiences, pics of the insides of the various alternatives for this saw.
Also, I would love to see some pics of what is needed to be done to fit the 044 carbs up to them.

 

[drf256]

Brews,

Your port work is outstanding. The true sign of a master is when people will look at a jug and think it wasn't touched. Your exhaust port is flawless.

Thanks for taking the time out to compare the carbs. I'm interested in how they may run differently.

 

[Brewz]

Thanks mate. I still need to cut the slot connecting the upper and lower transfers like I see done by the pro's

I will be cutting wood on Tuesday and will take the 026 and use it to give it some run in time and also to fine tune it.

For all intents and purposes I could find no difference between the the older 194 and the newer 394.
Only difference was the 394 has the different top that goes into the hole in the air filter to account for blockage. I have fitted this to the 194 carb.

When I change the spring out I will test RPM's before and after and record what changes needed to be made to the carb to fix the tune. This should help us understand what difference the metering springs are making

 

[drf256]

The "slot" is called a bridge port and I wouldn't cut it.

After doing a few 026 I've found it makes no difference. Most pro's agree that they are of little benefit in a 50cc saw.

 

[Brewz]

copy that!
Will save it for my 066

 

[Brewz]

When I first fitted the 194 carb, I set the L and H screws the the standard 1 turn out and it was so rich it wouldn't run.
It refused to rev up and just blew LOTS of blue smoke.
Leaned it out and got it to go.

I checked the screws on the 394 afterwards and both screws were set at about 1.5 turns each.

I guess that either the 194 is delivering buckets of fuel or the taper on the L and H screws is longer on the 394.

 

[drf256]

Or it's the metering spring.

 

[Deets066]

When I first fitted the 194 carb, I set the L and H screws the the standard 1 turn out and it was so rich it wouldn't run.
It refused to rev up and just blew LOTS of blue smoke.
Leaned it out and got it to go.

I checked the screws on the 394 afterwards and both screws were set at about 1.5 turns each.

I guess that either the 194 is delivering buckets of fuel or the taper on the L and H screws is longer on the 394.

Did you measure the Venturi? Or just eyeball it? .020 different Venturi could possibly suck fuel at a higher rate

 

[Brewz]

Ah yes....... and this is why I have started this thread.

 

[Brewz]

0.001 difference

194: 0.533
394: 0.532

 

[stihl saws]

The springs are interesting. I recently swapped a WT-194 onto my 260. It came with the 394, which was running fine. The bores mic practically the same, yet the saw feels snappier with the 194.

 

[Brewz]

Yeah they are very different springs...... there has to be something in it.

From what I have learnt thus far, a stiffer spring will change the fuel delivery curve on the L circuit.
The heavier spring is meant to lean the saw out more at idle, allowing you to increase the opening of the L screw. The theory being that it will now throttle up faster as its kept leaner down low, but the L circuit will then supply more fuel in the cut as revs drop under load, propping up losses from the H circuit which has a peaky fuel delivery curve.

At this stage its theory as far as my knowledge and experience goes, and I am trying to get some practice insight into what works best in the cut.

In other threads, the argument has been weather the L circuit delivers fuel at WOT and at loaded cutting speed at all or if it is propping up the H circuit as revs drop.

Very hard to really know exactly whats happening.

 

[stihl saws]

It would be interesting to compare the needles to see if there is any visual difference. The difference between the carbs on my saw simply can't be a slight difference in tune. It's noticeably stronger with the 194. I just can't explain why.

 

[Duane(Pa)]

Awesome thread BTW

 

[Redfin]

I messed around with a slight bog off idle on my 194 for weeks. Turned out this saw likes a little higher pop off pressure. I suppose a spring swap would have solved it but just lowered the arm a hair.

Edit: maybe the spring is just weak.

 

[czar800]

Brewz, great info. And your work looks flawless. You're the carburetor guru.