Stihl MS260 Over-Fueling??

[hawthornheavyhorses]

Thanks Barrie, will send you a PM about some other bits too.

 

I tried the saw quickly again today, but after trying a plunge cut and pulling the plug it actually seems to be running a bit lean as it looks a bit white/grey. More worried about this as I don't want to damage the saw now it's running, so really want to get a tacho on it. Not sure I trust my ear on it, I can hear it picking up as I screw in the H, but not sure I can detect it 4 stroking (possibly too many years playing in bands as a teenager!!)

 

Out of interest, the handbooks gives you the standard settings for the H and L screws, but is there a standard setting for the LA screw? Guessing that this needs to be correct before adjusting the L.

[GardenKit]

Thanks Barrie, will send you a PM about some other bits too.

 

I tried the saw quickly again today, but after trying a plunge cut and pulling the plug it actually seems to be running a bit lean as it looks a bit white/grey. More worried about this as I don't want to damage the saw now it's running, so really want to get a tacho on it. Not sure I trust my ear on it, I can hear it picking up as I screw in the H, but not sure I can detect it 4 stroking (possibly too many years playing in bands as a teenager!!)

 

Out of interest, the handbooks gives you the standard settings for the H and L screws, but is there a standard setting for the LA screw? Guessing that this needs to be correct before adjusting the L.

It is much more common to have a weak mixture than a rich one as there are more faults that can cause it. It is also much more detrimental to the saw, so dont use it until its tuned. The 261 needs to be tached to 14000 but even after that I like to check that its just starting to four stroke as its possible that due to wear and tear the saw just wont reach 14000 unless running weak.

 

The LA screw does not have an initial setting, but what you do is start the saw and warm it up. Set LA to a slightly fast tickover (3600) Turn L in to get max eng speed (weak) If this is over 3700 then start again.

Then set LA down to 3300 and then tune L screw out (rich) to 2800 rpm.

The above instructions come from the Stihl manual.

 

In practice, I do it by ear, set LA a little high, tune L in to 'lean drop off', this is where speed has peaked and just started to drop off. Then turn L out to ' rich drop off ' then turn very slightly to lean, which is where the engine reaches its lowest stable speed.

At this point the engine should pick up immediately when the throttle is blipped.

I then set the LA to an even tickover just below the point at which the clutch starts to engage, i.e the chain is not attempting to turn, and check the tune again.

 

The movement on the L screw will be very slight between the drop off points so turn it very slowly.

The clutch engagement point can be tricky if the clutch springs are worn as the engine speed may be too low to keep running, hence using the tach.If the chain moves at 2800, replace the springs.

Hope this helps, and I hope I have not missed anything out.

[hawthornheavyhorses]

Thanks Barrie, very helpful and really appreciated, will have a play tomorrow and see what happens! I certainly don't intend to use it until the carb is set up properly, but am I likely to do much damage adjusting it and testing it on a log? Any precautions I should take?

[GardenKit]

You will be Ok to test it. With what you know so far set the h screw to the richer end of the limits and you wont do any harm whilst tuning the low end, but you still need to get the H screw properly set before working the saw.

[spudulike]

Sometimes when you are new to this it is worth taking the H screw out - around two turns and you will hear the fourstroking in abundance - then when you turn the H screw in, you will hear the saw clean up on the top end and the fourstroking become les and less, the art is in making sure it is still there and the saw isn't over revving.

 

If you are not happy with the plug colour, take the screw out 1/4 turn and try another cut and see what colour the plug is.

[hawthornheavyhorses]

Ok, my Tiny Tach arrived in the end today, I've set up the idle as Barrie described and it is now idling very nicely at 2800.

 

However it on WOT it is reving to 14400+, so is running a bit lean!

 

So I have 2 choices, I can take off the limiter cap so I can rich it up a bit, or I can pull the carb again and lift the meter arm a little.

 

One thing I did remember today, was that the limiter cap may not be set to 100% factory setting, because after I ran the saw in my instructor at the time put a tach on it and it was running a bit lean and he couldn't adjust it out, so I took it back to Stantons and they removed, tuned and put it back in again.

 

Any thoughts would be appreciated!

[GardenKit]

Glad you got it going well. With regards to WOT, my opinion would be to take the limiter off and tach without it. I would use the tach, but also double check it with basic principles of 'fourstroke setting' as described before. Hopefully the two methods should produce the same result

Others may agree or disagree.

[spudulike]

Glad you got it going well. With regards to WOT, my opinion would be to take the limiter off and tach without it. I would use the tach, but also double check it with basic principles of 'fourstroke setting' as described before. Hopefully the two methods should produce the same result

Others may agree or disagree.

Agree 100%

[GardenKit]

Just thought of something else. The bar and chain must be on the saw with the chain properly tensioned whilst tuning. This drags the revs back a bit.

I know it seems a little patronising to state this, but I have known people try to tune without the chain as they can be a little scary zipping round at 1400 rpm on your bench.

Take care to have a clear bench and keep a firm grip on the saw, and ensure good ventilation.

I sometimes clamp the handle to the bench on the bigger saws with more 'gyro' effect.

[hawthornheavyhorses]

Thanks guys, limit cap comes off in the morning then!

 

Yes chain is on and tensioned up, but best to check!

 

Will let you know how I get on.