Inside the 441 M-Tronic Carb.

[Miles86]

Probably because industrial electronics have an average lifetime of let's say 7 years....just guessing. He must have seen $$$$ in the future..., can't really blame him.

Exactly- I'm old enough I don't need to have added problems with a chainsaw with that on it, I have enough fun tuning my regular carbs. I understand why they (Stihl etc...) are doing it, I just don't care to be part of that if it doesn't add any real value to (me).

 

[Chris-PA]

The controller for the stepper solenoid is in the ignition module. I would expect the components for the ignition to be under far more stress than the parts for the carb control. There's no telling if they did a quality job on the design of the controller, but if done properly it should last longer than the ignition. I say that as someone who has designed industrial power electronics for 25 years.

The added value of the system is that it provides a fuel system that can hold a correct fuel/air ratio with varying load, as well as with varying atmospheric contritions, which your traditional carb cannot do. This means it makes more power under a much wider range of conditions, uses less fuel, as well as not burning your piston should you happen to increase the load further than the point where you set the mixture.

 

[Tzed250]

Excellent information!!!

 

[porsche965]

Thanks for taking the time and pictures.

Great information.

 

[eiklj]

Convert to M-Tronic

Got the carb all put back together today. I put a new gasket kit in it just to be safe. The old gaskets looked fine but not a big deal to replace them while I'm there.
So from what I can tell here's all you need to convert your 441 to an M-Tronic. The IPL shows the same part number for the flywheel. I don't have any pricing in our system to know what the individual components would cost should somebody want to do a conversion.
View attachment 252743

jason

 

[naturelover]

Thanks for the pics!!!

Great information!

 

[s219]

So what powers the electronics?

 

[Chris-PA]

So what powers the electronics?

The big spinning magnet in the flywheel can also be used as a generator - they don't need much power.

 

[Somesawguy]

I think the weak point in those systems will be corrosion and connection issues. The "injector" connection looks especially prone to issues once you get a little corrosion on the PCB trace. Was there any silicone grease or other protective coating on the connections?

 

[eiklj]

I think the weak point in those systems will be corrosion and connection issues. The "injector" connection looks especially prone to issues once you get a little corrosion on the PCB trace. Was there any silicone grease or other protective coating on the connections?

None. And I did not put any on when I re-assembled it.
I was supprised not to see a much finer fuel pick-up filter as any crud at all would easily plug such a small actuator.
I know with electro-hydraulic proportional control systems, the filters need to be around 10~15 micron or less. Otherwise you can clog those passages.

 

[eiklj]

So what powers the electronics?

I didn't measure anything, but I would assumbe you're dealing with milliamps of power at say, 0~3 or 0~5 VDC so not much power is required to operate.
Making the ignition spark jump the gap uses way more power than what the electronic brain uses.
I would like to hook up a scope on that once it's all togehter just to see what's happening.

 

[user 64030]

opcorn:

dw

 

[LowVolt]

Got the carb all put back together today. I put a new gasket kit in it just to be safe. The old gaskets looked fine but not a big deal to replace them while I'm there.
So from what I can tell here's all you need to convert your 441 to an M-Tronic. The IPL shows the same part number for the flywheel. I don't have any pricing in our system to know what the individual components would cost should somebody want to do a conversion.
View attachment 252743

jason

Awesome write up man! I am not doubting you at all but can anyone confirm this?

 

[blsnelling]

So, what in these carbs would cause a ported saw to run rich at idle? The saw runs fine at WOT. At idle, it is a little erratic, but not bad. The wildest part is that, when you pick it up off the ground, it will sometimes die. Throttle response also stutters. It improved a little by raising the needle lever, but the problem remains.

 

[LowVolt]

So, what in these carbs would cause a ported saw to run rich at idle? The saw runs fine at WOT. At idle, it is a little erratic, but not bad. The wildest part is that, when you pick it up off the ground, it will sometimes die. Throttle response also stutters. It improved a little by raising the needle lever, but the problem remains.

He mentioned in post #3 about a factory set idle speed screw.... Does that have anything to do with your problem?

 

[blsnelling]

He mentioned in post #3 about a factory set idle speed screw.... Does that have anything to do with your problem?

The problem is that it's too rich, not idling too low.

 

[Chris-PA]

So, what in these carbs would cause a ported saw to run rich at idle? The saw runs fine at WOT. At idle, it is a little erratic, but not bad. The wildest part is that, when you pick it up off the ground, it will sometimes die. Throttle response also stutters. It improved a little by raising the needle lever, but the problem remains.

If the carb is running open-loop (non-feedback) at idle, which I think is likely, then what sets the idle mixture? It's probably preset for that saw.

Also, If your ported saw is drawing significantly more air at low rpm, it may be creating a strong enough pressure drop to partially activate the main circuit at idle, enriching the mixture. If it's not in feedback mode it won't care and won't try to correct the mixture.

I had a similar situation with my SE3420, and had to put on a carb (HDB series) with a bigger venturi. With smaller carb if I opened the L screw more than 1/4 turn it would flood out.

 

[blsnelling]

FYI, I ported another that's almost identical. It initially exhibited similiar symptoms. I made the following two minor adjustments, reinstalled the carb, and the problem disappeared. I slightly raised the needle on it. Also, there's a small adjustable set screw that's set in plastic, off to the left side of the carb. It adjusts against a metal stop and affects when the clean air butterfly opens. I set the screw such that it barely protrudes and just touches the metal. That adjustment hasn't yet been made on this second saw. I'm hoping that it corrects the issue. I'm wondering how pop-off pressure would affect this. Unfortunately, this second saw didn't exhibit these symptoms until it was at it's new home.

 

[Chris-PA]

Would that be propping the clean air valve open further, or "advancing" it?

 

[blsnelling]

The more you screw it in, the sooner it opens the butterfly. Also, the stutter got worse and worse the farther I moved it in.