Mastermind Revisits The MS261CM Type II

[Mastermind]

It's all his fault.

 

[RI Chevy]

He's a sum *b-word. LOL

 

[wcorey]

While I get what’s going on in principle, I still have a difficult time getting my head around how it determines (what they term as) the ‘desired operating point’, based on RPM only, without knowing the throttle position.

I see how it makes the changes to get there, just not how it knows where that point is.
For instance, how does it know when to idle rather than finding max RPM under load?
(EDIT: Oh never mind that example, just occurred to me it's got minimal air coming in at closed throttle, so of course adjusts mix/adv accordingly. Duh. This stuff hurts my head...)

Some of the terminology in the patent was cracking me up, The ‘rotatably supported’ crank and ‘pivotably supported’ throttle plate… Is that stuff standard patent lingo or a bit of creative translation from German?
Some of it sounded like a lawyer rewriting the bible. Lol

 

[wcorey]

The venturi provides for the pressure/velocity differentials in the carb. Other than splitting the incoming volume of air into two columns, the divider has very little influence on that.

You'd think that to be the case but the reason I asked is because some here have stated an opinion that removing it does significantly alter the pressure signal to the jet to the point where it's near out of the range of adjustment...

 

[Mastermind]

You'd think that to be the case but the reason I asked is because some here have stated an opinion that removing it does significantly alter the pressure signal to the jet to the point where it's near out of the range of adjustment...

I think you my be thinking that the talk of gutting the stratos refers to removing the carb divider as well. I've nixed the dividing in the boot, and the jug, and even in the air filter base yet left the carb alone.

On both the 241, and the 261 there are gains to be had from doing so. The idea of such a radical change from the original design is not something I especially like doing though. I like the idea of using fresh air to purge the exhaust. I like the idea of less hydrocarbons in the faces of those that use these saw daily. So.......I look for ways to keep the design intact, and get solid gains. At the same time, I see no good reason to discount what anyone else decides is the best course of action.

You can bet I'll be doing even more testing and that I'll be trying new and different ideas........never should we stop trying to learn.

 

[blsnelling]

Was considering getting a 241, but when Stihl made the Ver II 261 lighter, I decided to go with that. A lot more grunt for a little extra weight

You still need a 241. With B&C and full of fluids, the 241 is a full pound lighter than the 261 VII. After porting they are a little beast. I sold my new 261 and pick up the 241 before my 346.

 

[wcorey]

I think you my be thinking that the talk of gutting the stratos refers to removing the carb divider as well.

Guess I need to go back through all this a few times, interesting stuff but a lot to digest with all the new saws coming out on top of it.

 

[Lightning Performance]

After 13 pages how is the biggest mystery the internal workings of mtronic and no one has asked how come Mike - after years of telling us that the lightest saw you'd ever need is a 10mm 044 (or maybe a 362) - has bought a 261.

Cad

I am still waiting for this.

Mtron good. Upsidedown divided intake trac good.

I've been using a popup in a couple models too....

Hahaha

Cheater

I believe you are mis quoting me, and have not been following recently.

If you can only take one saw with you, the 60 + 70 cc saws are the most versatile and can do anything, I will stand by that. My 60 + 70 cc saws are my work horses and get the most usage.

However, have you not been hearing my comments about my MOFO 026 Lightning Limber??? Love that little saw for the limbing duties, and now it will have a "partner in crime". The small saws are also more convenient to take along on the ATV. Was considering getting a 241, but when Stihl made the Ver II 261 lighter, I decided to go with that. A lot more grunt for a little extra weight.

I have been re arranging my saw portfolio, in an attempt to have 2 saws in each size from 50 to 90 cc (I count the 77 cc saws as 80 cc). I like to have a back up for every saw in case I rock a chain, etc. I currently have 3 066/660s, but one of them is spoken for. Since I have the 90 cc saws for milling, I sold two ported 77 cc saws (still have 2).

Skipped tldr

While I get what’s going on in principle, I still have a difficult time getting my head around how it determines (what they term as) the ‘desired operating point’, based on RPM only, without knowing the throttle position.

I see how it makes the changes to get there, just not how it knows where that point is.
For instance, how does it know when to idle rather than finding max RPM under load?
(EDIT: Oh never mind that example, just occurred to me it's got minimal air coming in at closed throttle, so of course adjusts mix/adv accordingly. Duh. This stuff hurts my head...)

Some of the terminology in the patent was cracking me up, The ‘rotatably supported’ crank and ‘pivotably supported’ throttle plate… Is that stuff standard patent lingo or a bit of creative translation from German?
Some of it sounded like a lawyer rewriting the bible. Lol

Stop making your head hurt. Buy a helmet soon!

I think you my be thinking that the talk of gutting the stratos refers to removing the carb divider as well. I've nixed the dividing in the boot, and the jug, and even in the air filter base yet left the carb alone.

On both the 241, and the 261 there are gains to be had from doing so. The idea of such a radical change from the original design is not something I especially like doing though. I like the idea of using fresh air to purge the exhaust. I like the idea of less hydrocarbons in the faces of those that use these saw daily. So.......I look for ways to keep the design intact, and get solid gains. At the same time, I see no good reason to discount what anyone else decides is the best course of action.

You can bet I'll be doing even more testing and that I'll be trying new and different ideas........never should we stop trying to learn.

Thanks for considering my lungs as much as the saws.

You still need a 241. With B&C and full of fluids, the 241 is a full pound lighter than the 261 VII. After porting they are a little beast. I sold my new 261 and pick up the 241 before my 346.

Tell me why? Sell me B-rad. What are the differences and how close are they after B-radification? We are cave men so you need lots of pics see...

 

[blsnelling]

Tell me why? Sell me B-rad. What are the differences and how close are they after B-radification? We are cave men so you need lots of pics see...

Here's the thread where I built it.
http://www.arboristsite.com/community/threads/snellerized-saws-re-visits-the-ms241c.288723/

Randy, if you want this in a different thread, feel free to remove this.

 

[Mastermind]

Randy, if you want this in a different thread, feel free to remove this.

This is a great place for it Brad. Adds to the discussion.

Thanks for sharing !!!!!!

 

[blsnelling]

BTW, if you want one, you'll have to get it from Randy

 

[Mastermind]

BTW, if you want one, you'll have to get it from Randy

That little dude is hauling ass.

 

[Lightning Performance]

Bring the info here too. I dont go there anymore. Are you going to give away the build as in the timing numbers in the port work you did to it?
You can keep your secret pics of the grindings.

That saw flies.
If I get one mines only getting a muffler mod for now. So how does your 241 stack up against the 261 with just a muffler mod?

 

[Lightning Performance]

I looked to page one. You gutted the stratos. I'm not building a gutted saw but Thanks.

 

[hseII]

And that is @blsnelling fault for sure

That damn Brad.....

Bastard

It's all his fault.

He's a sum *b-word. LOL

Yep.

 

[Wonkydonkey]

Bring the info here too. I dont go there anymore. Are you going to give away the build as in the timing numbers in the port work you did to it?
You can keep your secret pics of the grindings.

That saw flies.
If I get one mines only getting a muffler mod for now. So how does your 241 stack up against the 261 with just a muffler mod?

don't go where ??

 

[T.Roller]

Yep.

Exactly

 

[retro]

You'd think that to be the case but the reason I asked is because some here have stated an opinion that removing it does significantly alter the pressure signal to the jet to the point where it's near out of the range of adjustment...

That is true because removal of the divider from the carb increases the venturi diameter/area and allows a greater volume of air to pass through the carb past the fuel supply jets/nozzles. As gross venturi area increases for a given displacement engine and RPM, the pressure increases and the velocity decreases.

Its the same effect you'd get if you doubled the size of the carb, but installed jets in that larger carb matched for a carb half its size. To fix it you'd need to rejet/recalibrate the larger carb... assuming the larger carb flow capability is a decent match for the engine displacement and RPMs it will be operated at.

 

[retro]

While I get what’s going on in principle, I still have a difficult time getting my head around how it determines (what they term as) the ‘desired operating point’, based on RPM only, without knowing the throttle position.

That is an excellent question! It functions by monitoring RPMs only. No other data is available for it to analyze and it doesn't require anything more. Once the engine reaches a predetermined upper RPM point (that RPM point is hard-coded into the instructions for the processor) the system begins to optimize timing and mixture for WOT operation. Below that predetermined WOT RPM point, timing is being retarded and fuel supply is decreased so that the motor may idle smoothly. The carb itself works like any other conventional carb does (no requirement for electronic control), because it contains conventional low and high speed jetting circuits... the saw operator controls the carb (engine speed) with his/her trigger finger which provides for engine loading response. Only the available fuel supply for those high and low speed circuits are being altered while the motor is running.

 

[blsnelling]

I looked to page one. You gutted the stratos. I'm not building a gutted saw but Thanks.

Don't be skeered