Stihl 026 carb help

[Mike mandry]

Was out cutting with the 026 today.

Last time I ran it it seemed a little lean on the top end.

I got the carb dialed in the best I could & got it running great. Checked the plug & it looked like it was right in.

Ran about a half tank through it & now its giving me trouble again.

The darn thing falls on its face about halfway though a cut.

It idels fine, runs fine into the start of a cut & them its like it just slows down to nothing. Adjusting the H screw does it no good.

Let it sit & make another cut & it will do the same thing.

Saw is stock except for a muffler job & a WT 426 3 screw carb.

Carb is new. I might have half a gallon through it.

Im going to check the usual. I think the carb is FUBAR & needs a rebuild (best guess)

Tank vent & impulse hose are my first suspects after the carb. However loosening the fuel cap did not help it any.

Any ideas ??

 

[Four Paws]

Is the WT426 Walbro used on the 026/260 saws? I am not a Stihl guy, but if it is just the fully adjustable version - no worries there. If it is off a different make/model of saw, it might not have the proper flow/fuel metering the saw needs. That said, the obvious things to do are:

Rebuild the carb, make sure you replace or clean the screen!
New fuel filter
New fuel line
Check the impulse hose (if it is bad, it usually won't idle).

Do the above, and the saw should run like a top again.

 

[Mike mandry]

The carb is brand new.

The ful line looks like it might be a little kinked,however its always been like this & no issues in the past.....

 

[Lakeside53]

It could also just have a bad crank seal under the flywheel.

The fuel line looks fine.

 

[Mike mandry]

Pulled the carb apart & it was clean.

This is a low hours saw. Still has the orig bar & chain, so I cant see how the crank seals would fail already, although I have seen stranger things.

I pulled the muffler & piston & rings are fine. Actually running a bit rich if anything.

It seems as if it is starving for fuel after you get about 4 seconds in to a cut.

Back it out & let it idle & make another cut - it will rev up to speed & cut with full power & then repeat this all over again.

The carb that is on it has less than a half gallon through it. I run 93 with Mobil MX 2T @ 32:1

How tight should the band around the carb boot be where it goes on the cyl ?? I checked it & while not loose, it sure wasn't snug.

 

[Scandy14]

Tightness of clamp on intake boot

Mike,

The hose clamp should be tightened so that the gap between the two ends of the clamp is 3.5 to 4.5 mm.

 

[Four Paws]

Bad clutch? I seriously think a carb rebuild is in order. If it doesn't work, you are only out like $6 for the kit.

Usually a bad crank seal will make the saw rev high as air is leaking in = leaning the saw out.

 

[Lakeside53]

A bad crank seal can do exactly what is described.. With a leaky seal the carb pump can supply enough fuel for low rpm but not as the needs increase. 4 seconds - that's just emptying the full metering chamber...

Check you fuel hose inside the tank. If it's sucking air near the top you'll get the same effect.

If you want to prove it's the carb and not the fuel line etc, just connect a small tank directly to the carb and hang it about 3 feet above the saw. If it runs, ok at your seals/impulse, etc.

 

[Mike mandry]

A bad crank seal can do exactly what is described.. With a leaky seal the carb pump can supply enough fuel for low rpm but not as the needs increase. 4 seconds - that's just emptying the full metering chamber...

Very good point, I think you might be on to something there. Makes perfect sense to me.

 

[Mike mandry]

Lake: How difficult is it to replace the crank seals ??

I assume the clutch side is more difficult.

Can I strip it down to the point where you can access everything (remove flywheel, clutch oil pump & etc..) & take it to the dealer vs having them do the whole job.

 

[Lakeside53]

Without the right puller it's a PITA.. with the right tool it's a breeze.. The clutch side is actually easier as the seal is larger and there is little chance of damaging the outside surface as it's part of the bearing. YOU can often just deform it with a punch and it will pop out. The clutch side is difficult as it's very tight and if the seal gets pushed down you'll need to split the crank case to get it out even if you have the "right" tool! The clutch side rarely fails on the 026.

I wouldn't go replacing seal unless you've done a pressure/vac test. Do the external fuel tank test I suggested - just a can and 3 feet of fuel hose...

Yes, If you have a friendly dealer, that would work. But also pay them to pressure test it.. Before to make sure it is seals or whatever, and afterwards to make sure the seals have integrity.

 

[Mike mandry]

Thanks for the info, I really appreciate it.

If I get time to fool around with it today, I'll let you know how it goes.

 

[Mike mandry]

Well, I think I got it.

Swapped out the carb for another new, never used WT 426 that I had.

Started at 1 turn out on the H & L

Ran about 2-1/2 tanks through it & its running pretty darn good.

The only thing I notice is that most of the time it will take about a full 10 seconds after a cut for the chain to stop (engine to slow down enough for the chain to stop) Once it idles down it will stay there & idle all day long.
Runs great in the cut as well.

Got the carb dialed in & made a few good runs, shut it off & pulled the plug. It looked pretty good, so Im going to call it done.

Im not used to a saw taking that long for he chain to come to a stop. Is this normal, or the beginning of a problem.
Im used to running old Homelites & macs, so this is new territory to me.

Ive had this saw for about a year, but have not really used it all that much yet.

 

[Lakeside53]

Long slowdowns are a clear indicator of a slight air leak... Like a seal on the way out. I'd pressure and vac test it.