Mastermind Revisits The MS261CM Type II

[blsnelling]

A lot of factors at play, but the way I was thinking of it, if total volume is the same, or almost the same, velocity would be reduced which would reduce vacuum at the venture. The jet size would need to be increased correspondingly.

I believe this is correct.

I think you misunderstood Randy's original question though. He asked what would happen if you enlarged the intake tract.

 

[Mastermind]

I THINK....By removing the divider, you're causing less fuel to be drawn through the nozzle. MTronic does not have a wide enough operating range to be able to compensate.

I agree.

By removing the divider you are doubling venturi size, so it loses its ability to supply enough fuel.

 

[Mastermind]

FYI, you can remove the divider from the carb of a non-MTronic saw and still tune it to run properly. However, you end up with the H needle much further out. MTronic just can't compensate that much.

Exactly.

But....I've not found any gains in removing it in the non M-Tronic versions either. As you say, it just changes the position of the high speed needle.

 

[paragonbuilder]

RPM, RPM, RPM. The way I understand it, it tunes for max RPM, whether it be lean or rich. The only feedback it has is RPM.

Nope

 

[blsnelling]

Nope

Please explain.

 

[MustangMike]

I'll explain, I've gone over the Stihl info numerous times, and it says a lot more than that, specifically:

"MTronic

The STIHL M-Tronic™ engine management system electronically controls the ignition timing and fuel metering in any operating condition, factoring in altitude and fuel quality. This system provides professionals with optimum performance, whether you are just starting to work or resuming after a break.

The STIHL M-Tronic continuously monitors the operating conditions of your chainsaw or brushcutter, calculating engine speed to continuously meter fuel. You save on fuel costs while experiencing optimum engine performance.

STIHL M-Tronic remembers your last setting under the same external conditions and resets to it every time once the engine reaches full power. "

Remembers your setting under the same external conditions ... That implies a lot more than just adjusting for RPM each and every time! It would be very easy to have temp and altitude embedded in there.

 

[Adirondackstihl]

“Calculating engine speed”

 

[blsnelling]

I'll explain, I've gone over the Stihl info numerous times, and it says a lot more than that, specifically:

"MTronic

The STIHL M-Tronic™ engine management system electronically controls the ignition timing and fuel metering in any operating condition, factoring in altitude and fuel quality. This system provides professionals with optimum performance, whether you are just starting to work or resuming after a break.

The STIHL M-Tronic continuously monitors the operating conditions of your chainsaw or brushcutter, calculating engine speed to continuously meter fuel. You save on fuel costs while experiencing optimum engine performance.

STIHL M-Tronic remembers your last setting under the same external conditions and resets to it every time once the engine reaches full power. "

Remembers your setting under the same external conditions ... That implies a lot more than just adjusting for RPM each and every time! It would be very easy to have temp and altitude embedded in there.

That says very little to explain HOW it works.

I can't find the documentation now, but Stihl explains it as I stated previously. That's not just my opinion on how I think it works...that came from Stihl literature. @paragonbuilder , if you don't think that is correct, please provide documentation otherwise so that we can all learn.

 

[MustangMike]

Why would it have a memory function if the operation was just so simple as to adjust to RPMs???

Clearly, it is a little more sophisticated than that. That is why it takes some time to learn changes, and why the saws seem to get stronger after numerous tanks of fuel.

 

[blsnelling]

“Calculating engine speed”

Exactly, although you kind of have to read between the lines. I wish I could find the documentation I'm referencing. It explains it very clearly.

 

[CR888]

Often it it advisable to errr on the small side when choosing a carb, as the stronger the signal the better throttle response and low end. But we all know how much top end you can gain from bigger carbs. Strato carbs are often divided with bigger venturi sizes per displacement compared to pre strato setups. I've played around putting strato carbs on older motors with good success. I often think whether dividers could make big carbs perform better than they normally would, strong signal down low, big flow up top! While their is no such thing as a 'strato carb' they have changed the way they carb a lot of strato stuff.

 

[MustangMike]

But you are correct Brad, I don't know exactly how it works, and can not explain it, but the literature and my experience with it leads me to believe it is a little more complex than what you stated.

It does not just instantly adjust to changes made based on RPM.

 

[paragonbuilder]

Please explain.

Damn it I was hoping to discuss this last night. I'm at work now.

I should have said IMO nope....
Sorry Brad

For starters if it only tuned for max rpm it would certainly go lean and would scream at WOT.

If I've read the literature correctly they have monitored the reaction of richening and leaning the Saw under load and how the Saw reacts, they have written that into an algorithm that monitors multiple times a sec, and adjusts accordingly.

I could be wrong.

 

[blsnelling]

Why would it have a memory function if the operation was just so simple as to adjust to RPMs???

Clearly, it is a little more sophisticated than that. That is why it takes some time to learn changes, and why the saws seem to get stronger after numerous tanks of fuel.

Memory function? It simply leaves the solenoid set to its last position. Reading anything more into this is only guessing without documentation to back it up.

If never seen evidence that MTronic makes a saw stronger over time. People say the same thing about a saw bringing in. Break in is not a function of MTronic.

All I'm saying is, don't make this more complicated than it is.

 

[Mastermind]

But you are correct Brad, I don't know exactly how it works, and can not explain it, but the literature and my experience with it leads me to believe it is a little more complex than what you stated.

It does not just instantly adjust to changes made based on RPM.

Husky's system also uses a TPS. It's more complicated, and more trouble prone......

 

[breese]

According to the Owners manual it has the ability to change / save the optimal settings

"Under extremely changed operating conditions, attainment of the optimal setting can be accelerated as follows:
* Carry out five uniform cuts to length under full load"

 

[paragonbuilder]

I'll need to revisit this thread tonight unfortunately...[emoji19]

 

[blsnelling]

It does not just instantly adjust to changes made based on RPM.

That's exactly what Stihl literature said it does. I can't make any comments otherwise.

 

[Mastermind]

I know one thing for sure. Here in a little while I'm gonna post a video that will knock your socks right off.

 

[blsnelling]

What is there to save besides last solenoid setting and maybe timing? All it has to do it leave the solenoid at it's last previous setting. Saying that it has "memory" is just a fancy way of putting it that looks good on paper. Stihl marketing is genius.