Stihl 026 running erratic in cut

mjones · Oct 15, 2011

Have an early model 026 that belonged to my dad. Saw idles OK and will accelerate to WOT. As soon as saw is in cut the RPM start bouncing and saw bogs down. Fuel is fresh non-ethanol 89 octane with Stihl Ultra mixed 50:1, same fuel is being used in MS362 and Husky 142 and they are running fine.
I have replaced the fuel tank vent, new fuel line and filter,new air filter and new NGK plug. Tuned saw to 14000 rpm with tach. Saw starts within 4 pulls and runs to WOT without issue,but as soon as the saw is under load the saw start bogging down. Problem started last Sat in middle of cut on storm damaged tree. Was on third tank of fuel that morning when it started mis-behaving. Not sure why saw will run 14000rpm for several seconds and not skip a beat but just as soon as chain is in wood it starts running erratic. Any ideas?

o8f150 · Oct 15, 2011

the first i would do is check compression to see where it is at

PA Plumber · Oct 15, 2011

If the saw has decent compression, I'd look at replacing the impulse line, checking/replacing the carb/intake boot and installing a new carb kit.

alderman · Oct 15, 2011

I had a saw doing that and it turned out to be a partially plugged screen in the muffler. I'm not a mechanic and most likely not your problem, but it is an easy thing to check out. Out of the wood, my saw was acting normal.

mountainlake · Oct 15, 2011

Could be a fuel supply cause or just set too lean, try `13000. Steve

mjones · Oct 15, 2011

mountainlake said:
Could be a fuel supply cause or just set too lean, try `13000. Steve

Have tried 12800 -14000 no change. Saw runs best @ 13,800-14000

w8ye · Oct 15, 2011

I had a Dolmar 111i that would do that and it was the high speed nozzle check valve in the carb.

I installed a new carb. This past week I ran 3 gallons of fuel through the saw and no problems except having to stop and put gas and bar oil in it.

mjones · Oct 15, 2011

Pulled muffler and was clean , almost no carbon . Thought is was amazingly clean for a 20 year old saw, pretty sure muffler had never been off . Took a look at side of piston and rings while i had muffler off. No carbon residue that I could see. Someone suggested change impulse line but I am not familiar with this. i know that it is a hose that comes from crankcase but not sure if it goes to fuel tank or carb. Any pointers on impulse line? not sure of location

mjones · Oct 15, 2011

went to local O'reilly auto parts and bought can of Seafoam. Took off air cleaner and poured into carb, pulled throttle and let it go down in intake and set for couple of minutes. Had to pull rope probably 10 times before it would fire. White smoke everywhere but did seem to be less erratic. Stopped saw and poured probably 1/8 oz. into fuel tank and filled with fuel. Cut several rounds from 10" seasoned maple log I had and there is definitely some improvement. Probably 80% of normal operation. Pulled air cleaner and poured another shot of Seafoam down carb and re-installed air cleaner. will let set over night and try again tomorrow.

jus2fat · Oct 15, 2011

Sure sounds cool so far..!!

I have heard / read about Seafoam and seen videos of the "white smoke" thing.
Kind of a WTF thing for sure seeing all that smoke on youtube videos...:msp_scared:
I'll buy some to keep handy next visit to auto part store...!!
Best of luck..!!
:cheers:

J2F

ZeroJunk · Oct 15, 2011

Sound like it was a carb issue if the Sea Foam helps, perhaps a partially stopped up orifice, needle metering lever set incorrectly, diaphram worn, whatever.

I still wouldn't turn that saw 14000 if it was mine. Sort of flirting with a burnt piston for little gain. IMO anyway.

mjones · Oct 15, 2011

ZeroJunk said:
Sound like it was a carb issue if the Sea Foam helps, perhaps a partially stopped up orifice, needle metering lever set incorrectly, diaphram worn, whatever.

I still wouldn't turn that saw 14000 if it was mine. Sort of flirting with a burnt piston for little gain. IMO anyway.

Slowed saw to 13700. Owners manual and shop manual list max. @14000. When I brought it home from my dads I thought saw was running a little fast. Put tach on it, running 15,600! Pretty sure that high speed jet had never been touched. Did it come from Stihl that way? not sure but it was stroking.

THALL10326 · Oct 15, 2011

Since you say it starting acting crazy all the sudden do alittle check on your wiring harness. 026's, especially old ones, are well known for the wiring harness to ground to the crankcase right at the top engine bushing near the carb on the left side. There is a metal clip that holds the harness in place. Its right at that clip that the wires tends to get a bare spot and ground the to the crankcase. It comes from vibration over a long period of time. Most cases the saw will run fine in your hand but under a load it will act up. Reason it does is because its being partly grounded out, under a load the plug has to have full ignition to fire correctly, in the hand under no load it doesn't. Check out those wires for any cracks or where the rubber coating has worn off. That saw would run best right at 13,100-13,500 tops, anymore is just alot of noise and no power gain at all..

mjones · Oct 16, 2011

THALL10326 said:
Since you say it starting acting crazy all the sudden do alittle check on your wiring harness. 026's, especially old ones, are well known for the wiring harness to ground to the crankcase right at the top engine bushing near the carb on the left side. There is a metal clip that holds the harness in place. Its right at that clip that the wires tends to get a bare spot and ground the to the crankcase. It comes from vibration over a long period of time. Most cases the saw will run fine in your hand but under a load it will act up. Reason it does is because its being partly grounded out, under a load the plug has to have full ignition to fire correctly, in the hand under no load it doesn't. Check out those wires for any cracks or where the rubber coating has worn off. That saw would run best right at 13,100-13,500 tops, anymore is just alot of noise and no power gain at all..

YOU THE MAN! Took a look at wiring and you were correct. Both black and yellow wires had insulation abraided and could see copper wire. Put some electrical tape around wires and that should take care of that. A bigger issue is the plug wire has a split about 1" long lengthwise also. Put some tape around it also but will replace it if I can find another plug wire. Are they replaceable? Slowed saw down to 13,500, saw purring like a 90 year old kitty cat now! :clap:

Thank you for yours and everyone else's help and suggestions!!

THALL10326 · Oct 16, 2011

mjones said:
YOU THE MAN! Took a look at wiring and you were correct. Both black and yellow wires had insulation abraided and could see copper wire. Put some electrical tape around wires and that should take care of that. A bigger issue is the plug wire has a split about 1" long lengthwise also. Put some tape around it also but will replace it if I can find another plug wire. Are they replaceable? Slowed saw down to 13,500, saw purring like a 90 year old kitty cat now! Thank you for yours and everyone else's help and suggestions!!

Glad it worked out for ya. When you said it started all the sudden thats usually something that points to ignition. Carb issues tend to get alittle worse and alitte worse, not all the sudden like you described...

Mastermind · Oct 16, 2011

THALL10326 said:
Glad it worked out for ya. When you said it started all the sudden thats usually something that points to ignition. Carb issues tend to get alittle worse and alitte worse, not all the sudden like you described...

That my friends, is why Tommy is "The Champ" !!!!!!!!!

PA Plumber · Oct 16, 2011

THALL10326 said:
Glad it worked out for ya. When you said it started all the sudden thats usually something that points to ignition. Carb issues tend to get alittle worse and alitte worse, not all the sudden like you described...

Well Done Tom!

homelitejim · Oct 16, 2011

good to see THall posting again. I always enjoy reading his posts.

ZeroJunk · Oct 16, 2011

find another plug wire. Are they replaceable?

It should just screw in to the ignition module. A decent dealer will have them.

chopperfreak2k1 · Oct 22, 2011

homelitejim said:
good to see THall posting again. I always enjoy reading his posts.

yup, ALWAYS enjoy reading his posts

Stihl 026 running erratic in cut

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