Stihl MS 441 Mods and Results

[parrishturf]

I am new to posting so bare with me. I have had some success hopping up a 441. And question some of my results. Can anyone confirm or refute any of the following: (I am shocked this saw stayed together, it's remarkable)

Pre mod stats:
Max rpm 13,000 open shaft
140 psi Comp
Throttle response B-
Saw is high milage

Mods:
+10% Width Intake and Exaust Port.
Open and smooth all passages.
Taper ends of transfer ports under jug, and open to match case opening. (I have not knife edged the bridge between frt and r ports yet, just radiused.)
Enlarge and port match Fuel intake, Air/Strato intake, exaust.
Enlarge radius on jug skirt to allow smother flow to transfer ports.
Removed base gasket.
Drilled Muffler in stages Stock, +1 3/8" hole then, +2 3/8" holes, left original port open.
Did not remove Choke plate.

Results:
OMG!!!
The muffler drilling added about 750 RPM each port.
The base gasket took compression from 140 to 175 and no leakdown at 1min.
PlayDoe Squish test yields clearence all around top of piston, But close.
Final open shaft rpm 15760 tuned lean with no burble.
Carb settings for 13500 or even the high and lean 15760 were surprisingly tight.
Throttle response A+, cranks on 1/2 choke first pull.

Maybe to much info but, I did not think this saw with the strato ports would even run on the stock carberator after opening everything up. The muffler mods are crude and worked well.

So here is my question, how can this saw, after opening every thing up, require tighter fuel settings?

Keep in mind this is no load data and all might change, but, after reading all the questionable performance gains that most have experienced, I thought I would ask a more expert group.

Future:

Slot flywheel Advance ???degrees
Polish and open carb.
Polish and open strato port.

If the engine wants more air the strato port might just do it...
I know there is a pot full of fuel left on stock carb...

All comments welcome...

 

[48"BAR PINCHER]

Sounds to me like you didn't do a very good job at all. Better send it to me ad I'll test 'er out for a while and make sure it's o.k.:greenchainsaw::greenchainsaw:

 

[Meadow Beaver]

What was your squish number? What do you mean " Enlarged radius on jug skirt"? Also the exhaust port being widened 10% isn't much. You should done a little more math on this. When widening the ports realize that you can go with in .020"-1mm of the piston skirt. Don't mess with the carb unless you really know what your doing. I don't know how you tuned it but with the stock carb you should richen it up, otherwise the saw won't get enough fuel to make the power it has, and could possibly seize. So just a few things to think about. Good luck, Mark

 

[nanuk]

I'm a little concerned also!

Sounds to me like you didn't do a very good job at all. Better send it to me ad I'll test 'er out for a while and make sure it's o.k.:greenchainsaw::greenchainsaw:

When he said "Final open shaft rpm 15760 tuned lean with no burble.
Carb settings for 13500 or even the high and lean 15760 were surprisingly tight".... I got thinking Oh Oh.... Lean seize! Probably scored things up pretty badly,..... he should send it to me, I need a "Practice Saw"

:monkey:

 

[parrishturf]

What was your squish number? What do you mean " Enlarged radius on jug skirt"? Also the exhaust port being widened 10% isn't much. You should done a little more math on this. When widening the ports realize that you can go with in .020"-1mm of the piston skirt. Don't mess with the carb unless you really know what your doing. I don't know how you tuned it but with the stock carb you should richen it up, otherwise the saw won't get enough fuel to make the power it has, and could possibly seize. So just a few things to think about. Good luck, Mark

No squish # yet, just confirmed clearence at this point. Port width conservative will increase in steps.

The radius is the cut-out in the cylinder sleave beside the transfer ports on base of jug. Thhis area looks tight to me coming up from the crankcase.

Thanks for the advice.

 

[Meadow Beaver]

Oh now grasshopper this is just the beggining for you. Just wait until you learn all the other stuff that can be done to a saw, then you'll never stop modding.

 

[stihlbro]

mmfaller, I've read enough of your post, and i am not sure you are contributing to the thread or being negative. What builds have you done. What tests have you done? You seem to ask alot questions but answer so sharply to others less informative to two strokes.Show some work or ease up on the new people. Geez man its Christmas. Grasshopper??????????????

 

[parrishturf]

At the risk of being redundant, my original question is still bothering me:

"So here is my question, how can this saw, after opening every thing up, require tighter fuel settings?"

After all the work mild and misguided it may be, has any one ever experienced a saw requiring less gas in the mix to run without loading up and bogging down?

This saw has only been bench tested to this point to see if its worth the effort to move forward.

I intend to continue on with more advance mods but wanted to take the work in steps. Everything I find written about this saw has unknown predictability.

I am willing to expose my failures with you if the data can help me or someone later. I get thease saw's for free and have the luxary to experiment.

 

[Meadow Beaver]

mmfaller, I've read enough of your post, and i am not sure you are contributing to the thread or being negative. What builds have you done. What tests have you done? You seem to ask alot questions but answer so sharply to others less informative to two strokes.Show some work or ease up on the new people. Geez man its Christmas. Grasshopper??????????????

No I'm not being an a-hole. He just doesn't have much for numbers so I can help the dude out.

 

[parrishturf]

OK... I will try one more time. Is there anyone out there with actual experience modifying a Stihl 441. Many of you have written reams of text stating all sorts of claims and some have stated experience.Help me have a technical discussion with someone. When I found this board I thought I had found a resource.

I will answer to the best of my ability any question to help you understand my question.

Just one question: Not how to... Not what if... Not well I'm...

"So here is my question, how can this saw, after opening every thing up, require tighter fuel settings?"

 

[zr900]

First off i am not a saw modder but have been reading about it for some time on this thread.

First check you squish. Just because you are not making contact does not mean you have enough room. Do some searching and find the recommended squish height unless you want to take a chance at blowing up your saw? I believe a good squish number is around .020 for a work saw, but you posted this in the hot-saw section so if that is what you are intending to do it may be tighter.

Second when you say your open shaft rpm do you mean w/o bar and chain? Bar and chain should be on to set rpm.

Third did you remove your limiter tabs on the carb to tune the saw? If not you won't have much adjustment.

Forth you said you tuned it to 15K+ rpm's to no burble. The saw should burble at WOT while running a bar and chain and then clear out when load is applied to the saw.

 

[PA Plumber]

Not a saw builder/guru/or even mildly intelligent about engine thingys.

Even when doing a small muffler mod, I have noticed the carb needs leaned out.

If what you have done is similar, albeit much more complicated, it seems a leaner carb setting would be required.

 

[matt9923]

I don't understand your question? After modding why not lean it out?

Please explain.

 

[2000ssm6]

For a work saw 441, 15760 is too fast. You either have a air leak or the stock 441's fuel system can't support what you have done. What does the plug look like? A few 441s have been ported and gained some great results. On this site, you could search for a member named "Treeslinger". His thread might help ya.

And where in NC are you getting these free saws? We need to meet.

 

[parrishturf]

Gentlemen:

Merry Christmas and thank you for the questions.

My concern was and is to avoid a meltdown. Yes this is open shaft testing, no bar and no chain. I was not expecting this saw to perform at all. I am concerned about the lean settings of H-1turn off stop & L-1Turn off stop. I have never had a saw with the adjusters this close to shut. (Yes limit caps are off)

I will continue with traditional testing, porting, etc. Especially tuning in oak. (Thanks for confirming the saw should burble free and clearup in wood. I agree with that)

The goal is max HP and Torque to limits of strato charge system. Or maybe 7hp!

Any info on timing advance, rekeying flywheel, or stihl compatable digital ignition would be nice...

 

[parrishturf]

For a work saw 441, 15760 is too fast. You either have a air leak or the stock 441's fuel system can't support what you have done. What does the plug look like? A few 441s have been ported and gained some great results. On this site, you could search for a member named "Treeslinger". His thread might help ya.

And where in NC are you getting these free saws? We need to meet.

You have hit on my exact concern. In the past when a saw is sucking air I was forced to give it all the fuel adjustment I could. I completly expected the strato porting to lean the saw out so much that it would respond exactly like a sucking saw. Or to have to close the choke to balance the two air paths. Instead no matter what I did each step made more power, all be it in my hand and not wood.

 

[matt9923]

I always tune with a properly adjusted bar and chains, you could break you saw runnign 15+ rpm with no load....

Just cut off the limiter cap tabs so you can adjust and its easier to get the screw driver in there as well as keep them from backing out...

After porting and any mods the factory 1 turn out doesn't matter, saw needs to be tuned to perform well and safely.

 

[porsche965]

Parrishturf,

Good thread started here. Be that it is the Holidays give this thread time for the experienced guys to get back and onto AS and I'm positive you will receive all the wisdom you are searching for. AS members can't be beat IMO.

I know nothing to help you but listen closely and follow the good advice received here.

Merry Christmas and welcome!

John

 

[Terry Syd]

Air flow

I have noticed a number of posts on the forum that have dealt with the need to 'lean' out the carb after doing some mods. It has to do with air flow. The increased air flow (velocity) through the carb creates a greater depression in pressure at the venturi. The greater depression draws more fuel from the carb and makes the mixture richer.

Check your plug to confirm that the mixture is correct.

 

[parrishturf]

I have noticed a number of posts on the forum that have dealt with the need to 'lean' out the carb after doing some mods. It has to do with air flow. The increased air flow (velocity) through the carb creates a greater depression in pressure at the venturi. The greater depression draws more fuel from the carb and makes the mixture richer.

Check your plug to confirm that the mixture is correct.

Terry:

Wil do... Keep in mind this is a strato charge engine, Dual flow path. I was expecting the air only path to pick up as well and cancel the additional richness. The plug is new and not coated with white soot. Should be enough fuel for now.

I think the strato charge is so short in duration that it has no effect over all.

Later when the ports are retimed to compensate for the base gasket who knows???

Thanks...