Pre 1998 Stihl 026 venting issue

[SteveSr]

So three choices:

• Use the existing vent or obtain a new one

A new vent of the same design will probably leak as much as the one that you already have

So three choices:

• Modify to use current Stihl vent part number 16 / 17

This will likely be harder than it looks. This one is made to press fit into a corresponding shrouded hole in the tank with the o-ring as a seal around the valve at the bottom of the well. You may end up with a bigger leak and no way to go back.

I would go look for a small brass hose barb that can either be installed from the top down or bottom up and glued into place. As you might guess this saw was never designed to be transported or used with the fuel cap pointing down.

BTW, a little tank pressurization won't hurt a properly functioning carb. The RVP is only about 10 PSI max for commercial fuel. I have yet to see a carb that will pop-off that low.

 

[PV Hiker]

Well said SteveSr. Keep it simple for multiply users not to screw it up. Pressurizing tank, I guess if a user experiences a fuel geyser condition, worst case the saw would flood out and die.

Old style tire valve stem for a wheel pushed up from the bottom and nutted down. Need to drill out slotted hole and attach fuel line to shaft is another thought.

I'll think of a way that users can't break it. If it was my saw the hose barb glued in would work, but these users would find a way to break it.

 

[SteveSr]

Old style tire valve stem for a wheel pushed up from the bottom and nutted down. Need to drill out slotted hole and attach fuel line to shaft is another thought.

Traditional Schrader valve stem would be too big for tubing to attach. However, a Presta bike stem with the valve removed and the threads ground down in the appropriate places would probably be close to the right size. Watch out as the tube material is nitrile so not very gas resistant. Can be cleaned off the metal stem with a torch.

Well said SteveSr. Keep it simple for multiply users not to screw it up. Pressurizing tank, I guess if a user experiences a fuel geyser condition, worst case the saw would flood out and die.

Fuel geysers are an unwelcome by-product of pressurized tanks. Keep the saw out of the sun on hot days!

 

[PV Hiker]

Went out to the shop this afternoon and pulled out a old Schrader valve. It is huge in diameter and overall length. I also thought of a Presta valve from back in my biking days. With the cover on there is not much room under the cover to have anything too big in size. The MS 290 vent is remote but at a 1 x1 inch it would not fit under the cover.

I took both screws out of the tall vent and blew it out again and this time the grub screw put some effort in screwing it in. The flow has slowed way down, but it still drips. Liquid molecules flow so easy.

I can make the effort to educate all users that it will leak when tilted with tanks down. With our True North scabbards, the saws are carried with the tanks down utilizing the padded patch on the inside of the bar. This is when I first noticed gas going all over the person back when it was carried. I have rubber vacuum nipple covers that the user could remove vent and push on to seal. Would work for some people but don't have confidence the others would get it and end up loosing the vent or packing it full of dirt.

I could try to use part number 22 and sleeve the hole or use a thin washer on the top side to make it snap in... hum-mm!

Will be working on this.... good thing is I have time as the trail is covered with snow for a while.

 

[drf255]

Strange tank situation. I’m wondering if a tiny washer or metal disc could be drilled to allow the red flapper valve to be maintained yet have a small enough OD to not fully cover the slots.

I’ve never seen one like yours. Generally the smaller slotted hole for the red flapper and the larger single hole for the black duckbill.

The red flappers are the same used in Holley carburetor accelerator pumps and can be bought for much cheaper that way. I think I got 20 for under $20 on eBay.

I had an 036 here that was leaning out hot. I went through 3 carbs and 3 fuel lines, many vac tests, etc... Finally looked in tank and saw that prior owner inserted the black duckbill into tank like the old flapper was. So the tank would vent pressure but hold a vacuum. That was annoying.

 

[PV Hiker]

Strange tank situation. I’m wondering if a tiny washer or metal disc could be drilled to allow the red flapper valve to be maintained yet have a small enough OD to not fully cover the slots.

All good in theory as the depth would be the controlling point using with a thin washer. Weld a plastic sleeve and drill it out. It is only plastic and anything can be modified (to a point).

The red flappers are the same used in Holley carburetor accelerator pumps and can be bought for much cheaper that way. I think I got 20 for under $20 on eBay

I thought they looked familiar.

I had an 036 here that was leaning out hot. I went through 3 carbs and 3 fuel lines, many vac tests, etc... Finally looked in tank and saw that prior owner inserted the black duckbill into tank like the old flapper was. So the tank would vent pressure but hold a vacuum. That was annoying.

That is annoying.

 

[PV Hiker]

Went out to the shop and measured the diameter of the hole where the red vent will snap into. It is 0.1" / 2.55mm smaller than the picture shows. I'll order a couple and see.

I put the 026 all together and warmed it up, cut some pies off test log. Adjusting "L" off of lean toward rich runs fine but push bar tip down dies. Make it way too lean solves it. Time for a carb rebuild and see if the screen is plugged up.

Really have to fiddle with L and LA who know how long this carb been running and what fuel. Has Stihl on cap and 32 on the throat have not pulled it yet.

Air filter fine, new fuel hose and filter. With Carb off will replace impulse line. Put bar in cut and twisted all around, no change in rpms.

 

[SteveSr]

I put the 026 all together and warmed it up, cut some pies off test log. Adjusting "L" off of lean toward rich runs fine but push bar tip down dies. Make it way too lean solves it.

Likely fuel pooling in the intake from too rich. Bar down dumps pooled fuel into cylinder and it dies. Yes, way too rich on "L".

Really have to fiddle with L and LA who know how long this carb been running and what fuel. Has Stihl on cap and 32 on the throat have not pulled it yet.

carb is likely a WT-22. Keep in mind that this saw is definitely old enough to have worn crank seals which may be one of the reasons that it is hard to tune. Can't tune an air leak! Left uncorrected the leak will get worse, saw will lean out and burn up!

 

[PV Hiker]

My thoughts too SteveSr. When I started it somebody had the idle way too high. The pooling gas tipped foward only clears up with L screwed in to the point of lean shutter at idle. Good running saw at top end and rips through wood!

At first when raised the bar tip straight up rpms would increase.

I do not own compression tester for 2 stroke just automotive ones and my vacuum pump has no gauge to properly check condition.

 

[Mad Professor]

How about a nylon male NPT barbed tube fitting that screws into the tank. Then fit a piece of tygon and two grub screws. Like a 038 stihl vent.

Real simple and cheap. $0.95

 

[PV Hiker]

How about a nylon male NPT barbed tube fitting that screws into the tank. Then fit a piece of tygon and two grub screws. Like a 038 stihl vent.

Real simple and cheap. $0.95

Very limited amount of space under the cover to fit anything other than the stock tall vent. Going to try the red vent from the bottom and leave the tall one in place. If not it is just going to run like as is for a while. Thanks

 

[PV Hiker]

As far as the rich running...

Had a peak at the cylinder intake and exhaust. Both sides look stellar and have no wear markings. Yea! The exhaust looks like it has been running rich for a long time.

The carburetor is a Walbro 22C . Took it apart and looks in great shape and clean. Just strainer had some minor crap, But that is now somewhere in the shop...darn it!

But as to why it was running rich I first thought the inlet control lever was out of adjustment, but it is at level height.

Then it hit me like a ton of bricks . The gasket, yea the one that sticks to the body and need to scrape off, is missing. Previous person did not install it.. So that allows the diaphragm to sit lower and keeps the inlet jet open dumping in more gas.

 

[Mad Professor]

Very limited amount of space under the cover to fit anything other than the stock tall vent. Going to try the red vent from the bottom and leave the tall one in place. If not it is just going to run like as is for a while. Thanks

If you screw that in flush, they only thing that sticks up is the barb, ~1". You can arrange the tubing anyplace there is room.

 

[PV Hiker]

Update on vent.

For $6 picked up part locally (1110 353 1600). Measured it and determined that diameter is fine. Depth was a little short so took some height from the plastic. Lubed it up and pulled it in. I did tear it as the picture shows. Should have smoothed out the plastic. Put the tall vent on and pulled vacuum on the gas line at the carb and air does come in. Will fill tank and cut some wood and see if I have any problems.

Update on Carburetor.

I was wrong... there is a gasket mated to the the diaphragm and appears to have been installed properly. Just looked so thin. Picked up a K10-WAT locally for $14 and did a complete rebuild. Have the saw all back together and if weather is fine tomorrow afternoon will give it a go. Hope that the carb will adjust better and not run rich. When I took off the air cleaner there was gas on the air cleaner housing, too much gas going everywhere.. I removed the impulse hose and it holds a vacuum.
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