Ms261 lean condition

[jurchybald]

Hello good people,
Im having difficulties with ms261. Brand new saw. Ported a cylinder for 261cm and found lean condition after. Did vac/pressure test, changed carb and still the same. Then I put this ported cylinder on brand new 261, delete limiters on carb and give it all the fuel necessary. Fresh fuel with good oil, right mix and everything. Still the same.
Pics showing jug after 2 min of runtime. I can easily scotch brite it to perfection but Im worried what would happen if I run it.
So my question is what have I missed. No obvious air leak, carb is tuned, how can this be? Saw is running just fine, idling well, four stroking before limiter kicks in.
And to make it even more confusing, new jug, not ported, from 261 that I put on 261cm had the same marks after few minutes running. Wtf??

 

[Shibby]

What oil/fuel mix? I usually run a heavy oil mix out of fear of running lean like you show, but I know asking fuel mix opinions of 10 people will get you 15 answers.

Did you port it yourself or have it ported by a known shop? If a shop they should be able to answer your concerns. If yourself, you might want to look at getting a bigger carb, but being a mtronic I don't know if a carb from say a 361 or 461 would work. I'm just throwing ideas out there.

 

[Stump Shot]

@huskihl

 

[Moparmyway]

You need to open the metering jet with a set of micro drills

 

[jurchybald]

Thanx for reply. I need some brainstorming at this point.
Mix is okay for sure we are talking about few min runtime. I'm pretty sure carb is not a problem on non tronic saw. It's four stroking hard. And I did few of them with same recipe,

 

[jurchybald]

Piston pics. 2min runtime
Im gonna cut the extension little more. There have to be a leak somewhere.
Does anyone have any clearence issues somewhere on this?

 

[NPKenny]

That doesn't look like lean seize signature to me. Of course, 2 mins run-time isn't even to temperature for metal expansion anyway.

That looks like non-chamfered ports or ragged ports. Something scratching or hanging.

 

[jurchybald]

Good viewpoint thx.
By 2min runtime I mean warming the saw first and than CUTTING for 2 min. I was not clear before.
Pics of beveled ports. They look better in real.
New saw, no dust in tank or glogged filter.
What else can scratch?

 

[huskihl]

Looks like most newer Stihls that have run for a few minutes. They always have some streaks but it never seems to get any worse. If you do run into lean issues after that or the saw sounds like it’s running out of gas and won’t rev up, it might be that the main nozzle needs drilled a couple sizes bigger.

 

[jurchybald]

This pics are after 1min of scotch brite polishing. There are some marks left but i cannot feel them under finger nail.
Do you realy think I should run it? I'm skeered

 

[huskihl]

This pics are after 1min of scotch brite polishing. There are some marks left but i cannot feel them under finger nail.
Do you realy think I should run it? I'm skeered

It’s normal. You can clean them off with Scotch-Brite and they will be there next time you look

 

[jurchybald]

Ok than, i'll run it tomorrow. Thank you

 

[drf256]

Streaking is normal, but those look excessive to me, especially the ones on the crown over the rings.

If it runs normally with a non ported jug, your numbers coulda increased the strato timing more that you thought.

Like the Kevin’s said, you may need to drill the jet bigger. Non ported ones don’t need that.

I’ve had issues with my mix on those. Oils with high viscosity at lower ratios (I had issues w Motul800) make an excessively thick mixture that won’t flow enough to feed the saw. It doesn’t happen on large saws because of the physical jet size.

Are you certain you base is perfectly square? Your porting looks great, so I am assuming your base is-but you never know. Side loading the slug can do strange stuff. I’d also rebevel with a diamond ball.

 

[jurchybald]

The non ported jug that I put on mtronic has exactly the same patterns as ported one on non mtronic saw. After 1 tank.

Base cut 1.1mm, running base gasket.

I have put bigger jet in mtronic yesterday.

Oil for testing purposes is orange stihl 50:1. I tried xp 40:1 same s**. Fresh gas 5% ethanol, it's what we have here.

Base should be in a 0.05mm tolerance, I ve checked it 50 times by now.

Ive been communicating with stihl rep who told me that mtronic V3 has no electronic limiter all done with selenoids. At list for 3 seconds than it goes lean. Have to check that.

Right now Im on my way to forrest with both saws 261 non ported and 261cm ported. Im gonna run both of them as hell. What will be will be. Gonna report back

 

[NPKenny]

What is the thought of Stihl rings being somewhat aggressive during the break-in period. are these streaks a sign of that?

I haven't worked on a new saw in a long time. When I reassemble a saw, I use a ton of 2-cycle oil, almost always Amsoil. Is there a chance that aggressive rings and Stihl oil at break-in leads to this signature?

 

[huskihl]

What is the thought of Stihl rings being somewhat aggressive during the break-in period. are these streaks a sign of that?

I haven't worked on a new saw in a long time. When I reassemble a saw, I use a ton of 2-cycle oil, almost always Amsoil. Is there a chance that aggressive rings and Stihl oil at break-in leads to this signature?

It happens in the bottom of the cylinder as well, all below the rings. I’ve cleaned all of it off and it’s there again after it’s been run. I believe it’s just an imperfection that shows up on the mirror-like plating. Whether it’s new and only test-fired from the factory or 10 years old with 1000 hours on it, they all look the same

 

[jurchybald]

They are both still running stock one is boring so only half tank through it. Ported one is crazy but lean in my opinion. Put 2 tanks through it. It has that annoying off throttle hessitation, lean on L jet.
I'm slowly giving up. Gonna switch jugs and port one for the mtronic more conservatively. Thinking about base cut only 0.5mm . That shouldn't add much to strato duration

 

[farminkarman]

They are both still running stock one is boring so only half tank through it. Ported one is crazy but lean in my opinion. Put 2 tanks through it. It has that annoying off throttle hessitation, lean on L jet.
I'm slowly giving up. Gonna switch jugs and port one for the mtronic more conservatively. Thinking about base cut only 0.5mm . That shouldn't add much to strato duration

Why not try opening up your main on the carb?

 

[Ketchup]

.

Or add duration to the mix intake.

What makes you feel it’s running lean?

 

[jurchybald]

I did that by changing main jet.