Stihl 026 problem

[stuartc44]

Hi everyone,

I have a Stihl 026, year 2000, which seems to have a small problem. I have tuned the saw to give a 'four stroke' sound at full revs which clears when cutting larger pieces of wood and the engine picks up quickly without spluttering. After a quarter of a tank or so the engine speed will remain on a fast tick over with the chain turning after cutting, and sounds to be running leaner on full revs when not cutting. I have tried opening the fuel cap to release any vacuum but no difference.

 

I have checked the fuel line, filter, impulse hose, carb manifold, new carb kit has been fitted, new stihl crank seals fitted and new spark plug.

 

When starting the saw with the choke it will fire after about five or six pulls and continue to run, not just fire and then have to use half choke as normal.

 

Is it possible it is a carb problem or does anyone have any other ideas?

 

Stuart.

[Mick Stockbridge]

Why would you want to tune it to give it a four stroke sound

Sounds like it's goosed to me, buy a new one and use it for spares.

[stuartc44]

The four stroke sound indicates that the saw is running a slightly rich mixture, this is for setting the high jet without a tachometer. A richer mixture is obviously better than a slightly lean mixture which would probably seize the engine.

[raker]

After 1/4 tank its up to temperature.Reduce your tickover untill the chain stops turning.Should be fine.

[Ian C]

Why would you want to tune it to give it a four stroke sound

Sounds like it's goosed to me, buy a new one and use it for spares.

 

[spudulike]

If you can, check for air leaks in the crankcase (crank seals), inlet boot etc, this can cause a high idle speed - bit like when you run out of fuel, same effect.

 

Well done for knowing about fourstroking at WOT - those guys taking the mick - he knows more than you do:thumbup:

Spud

[hazzygawa]

I know what 4 stroke is but what do you mean 4 stroking?

[stuartc44]

Thanks for that spudulike, will try checking again for air leaks.

 

4 stroking is a raspy blubbering sound when running at full throttle. for more info look here... Saw Carb Tuning

[lendahand]

Possible blocked exhaust, not sure but check it anyhow. Back pressure is critical on two strokes.

[spudulike]

I know what 4 stroke is but what do you mean 4 stroking?

 

A two stroke will fire on every revolution of the crank. If the carb is tuned too lean, it will fire on every revolution until 14-18k is reached and the engine goes BANG - it will heat seize due to the high level of revs, lack of fuel/oil mix being present between the piston and cylinder and the adverse heat being generated by exhaust and friction.

 

To stop this happening, the carb is tuned to run rich at around the 12k - 14k rpm level. This has the effect of leaving unburnt fuel in the engine on each stroke that means it stops the engine producing clean combustion on each stroke having the effect of only every other stroke producing normal combustion - something like a "fourstroke", this is the Blubbering sound you should hear on your saw at full revs.

 

Because the saw is underload when cutting, the saw is using the extra fuel at WOT to cut so the saw sounds fine in the cut!

 

Look at it as a rev limiter and oil feed all controlled by the carb:thumbup:

 

You did ask and that is why I said Stuart knows a bit more than most, not being rude or wanting to cause offence.

 

Cheers

 

Spud