SawTroll
Information Collector
One 372xpg is all I "had to" have, just for that reason - but maybe I should get more - like a 660 that I have no use for, just in case.........
MS280 . . . For Those In the Know About Stihl
- Thread starter Vernon Tull
- Start date
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One 372xpg is all I "had to" have, just for that reason - but maybe I should get more - like a 660 that I have no use for, just in case.........
Good discussion on new technology going on here...
Just to be sure everyone is up to speed on the MS 280 IEM, this carb is virtually identical to the adjustable WALBRO carb on the MS 270, MS 361, MS 390 and others, as far as how the circuits in the carb all flow. There is a low speed adjustable mixture screw that is dependent on the fuel it gets to feed through the idle progression holes from a fixed jet. This same jet also feeds fuel to the high speed nozzle, which opens and lets fuel into the venturi when there is enough pressure differential in the venturi to open the high speed check valve. This jet also feeds fuel to a mechanical accelerator pump that pushes a little bit of fuel up through the main nozzle every time the butterfly is opened to WOT. On the carb with a H screw, there is another small hole that feeds fuel to the H screw, and then that bit of fuel goes on to the main nozzle and into the venturi. The way to think about it is that the jet feeds about 80%, plus or minus, of the fuel the engine needs at WOT, and then the last 20% or so is adjusted by the H screw. There is also a part load jet, which is a stand alone circuit that has a metered jet size, a check valve, and opens up about half way between the last idle progression hole and the main nozzle, to help with off idle acceleration. All that has been done on the IEM carb is to replace the H screw with a digitally controlled solenoid valve that can be opened and closed up to 33 times a second to fine tune that last 20% or so of fuel. I like to think of it as a little guy with a screwdriver who is always tuning the carb for best performance as I cut through the wood, multiple times per second. If the engine needs more fuel it gets it, and if it is too rich it gets leaned out, all the time.
The advantages for the operator are that this carb will self adjust for a dirty air filter, variations in fuel quality, such as alcohol fuel up to E 10, altitude, and to some degree temperature and humidity and such. It also acts a little like a rev limiter. I ran a MS 280 IEM with no bar and chain, and when you hold it at WOT it revs up and then the IEM module pulls the RPM back down, even with no load at all on the engine.
I spoke to a dealer who works with smoke jumpers in the mountains. These guys are trying to put out a fire, stay alive, and having to adjust the carb on their saw as they move up and down the side of a mountain due to altitude changes. He felt that they would be glad to have this feature on a pro saw.
The solenoid is normally open, so a failure would have the engine running rich. If the signal between the solenoid and the ignition module fails, the module will turn off the ignition. The saw will start and idle, but shut off if the throttle is held open after just a few seconds. All the tech has to do to verify the solenoid and wiring is to take an ohms reading across the stop circuit wires with the air filter off. If it is open there is a fault, if the ohms reading is within range, it is good. Then take a 9 volt battery and connect it across the stop terminals, and there should be an audible click, just like checking the anti-back fire solenoid on a B&S engine. This confirms the solenoid is not varnished open.
I have cut with both a full adjust MS 280 and an IEM unit side by side and you really can't tell any difference.
As has been said, this will take away some of the things some of us like about being able to tune the engine, but it for those who just want to cut wood, this technology should give them better reliability and performance. I must admit that I really don't mind not having to tune the carb on my car anymore. But I do have a fully adjustable carb on the hot rod.
Change happens.
There will always be old saws around for those of us who like to tinker.
Just to be sure everyone is up to speed on the MS 280 IEM, this carb is virtually identical to the adjustable WALBRO carb on the MS 270, MS 361, MS 390 and others, as far as how the circuits in the carb all flow. There is a low speed adjustable mixture screw that is dependent on the fuel it gets to feed through the idle progression holes from a fixed jet. This same jet also feeds fuel to the high speed nozzle, which opens and lets fuel into the venturi when there is enough pressure differential in the venturi to open the high speed check valve. This jet also feeds fuel to a mechanical accelerator pump that pushes a little bit of fuel up through the main nozzle every time the butterfly is opened to WOT. On the carb with a H screw, there is another small hole that feeds fuel to the H screw, and then that bit of fuel goes on to the main nozzle and into the venturi. The way to think about it is that the jet feeds about 80%, plus or minus, of the fuel the engine needs at WOT, and then the last 20% or so is adjusted by the H screw. There is also a part load jet, which is a stand alone circuit that has a metered jet size, a check valve, and opens up about half way between the last idle progression hole and the main nozzle, to help with off idle acceleration. All that has been done on the IEM carb is to replace the H screw with a digitally controlled solenoid valve that can be opened and closed up to 33 times a second to fine tune that last 20% or so of fuel. I like to think of it as a little guy with a screwdriver who is always tuning the carb for best performance as I cut through the wood, multiple times per second. If the engine needs more fuel it gets it, and if it is too rich it gets leaned out, all the time.
The advantages for the operator are that this carb will self adjust for a dirty air filter, variations in fuel quality, such as alcohol fuel up to E 10, altitude, and to some degree temperature and humidity and such. It also acts a little like a rev limiter. I ran a MS 280 IEM with no bar and chain, and when you hold it at WOT it revs up and then the IEM module pulls the RPM back down, even with no load at all on the engine.
I spoke to a dealer who works with smoke jumpers in the mountains. These guys are trying to put out a fire, stay alive, and having to adjust the carb on their saw as they move up and down the side of a mountain due to altitude changes. He felt that they would be glad to have this feature on a pro saw.
The solenoid is normally open, so a failure would have the engine running rich. If the signal between the solenoid and the ignition module fails, the module will turn off the ignition. The saw will start and idle, but shut off if the throttle is held open after just a few seconds. All the tech has to do to verify the solenoid and wiring is to take an ohms reading across the stop circuit wires with the air filter off. If it is open there is a fault, if the ohms reading is within range, it is good. Then take a 9 volt battery and connect it across the stop terminals, and there should be an audible click, just like checking the anti-back fire solenoid on a B&S engine. This confirms the solenoid is not varnished open.
I have cut with both a full adjust MS 280 and an IEM unit side by side and you really can't tell any difference.
As has been said, this will take away some of the things some of us like about being able to tune the engine, but it for those who just want to cut wood, this technology should give them better reliability and performance. I must admit that I really don't mind not having to tune the carb on my car anymore. But I do have a fully adjustable carb on the hot rod.
Change happens.
There will always be old saws around for those of us who like to tinker.
Vernon Tull
ArboristSite Operative
Stihl #1 -- Good explanation and contribution. Very informative.
Peacock
Addicted to ArboristSite
Not to change the subject.....but the 4.0L V6 in an Explorer, Mustang or Ranger is not at all related to the 4.6/5.4/6.8 mod motors.
Eccentric
Mister Wizard
Thanks for the info. I'm curious though...How does the IEM system sense changes in altitude, air filter pressure differential, and fuel alcohol content? Does the saw have sensors such as MAP (Manifold Absolute Pressure), exhaust oxygen, throttle position, or engine/exhaust temp sensors? I thought (guessed realy, as all I have to go on is the Stihl brochures and info from you 'in the know' folks) that it just worked off of engine RPMS and a fixed set of parameters.
Boy, I have been out of the loop for a while. I didn't realize that modern saw carbs (regarding the non-IEM units) had that many circuits (and an accelerator pump on a small 2-stroke?). Sheesh. I'm still programmed for the older (what I'd consider conventional) Tilly, Walbro, and Zama two diaphragm 2-stroke carbs.
It's indeed true that 'Change Happens'. I still contend that there's Advances, but there's also 'Change for the Sake of Change'. The fun part is knowing the difference.
Perspective I guess...
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Eccentric
Mister Wizard
Realy? I thought they were at least part of the mod family. I don't mean you can swap heads and such. I was under the impression that the designs were similar. I remember when the 4.6L was first announced (years before it replaced the Windsor engines in the Mustang) that it was to be the first in a 'family' which would eventualy include a V6 and a V10. Oh well...Another subject where I was once 'in the know' and now obviously aren't... :censored:
Maybe this tangent of the discussion should be broken off and moved to the 'Rides' sub-forum...
elmnut
ArboristSite Operative
We have two Stihl 280 saws, no rave reviews, no major complaints either though. Not a bad saw to have in the line-up as far as I can tell. When the ms200 isn't enough I reach for the 441, why screw around?
Vernon Tull
ArboristSite Operative
Yes, Eccentric, I too remember that original plan you've mentioned here from Ford back about 1990 or 91 when they first began putting the 4.6L V8 in the Lincoln Town Car. I'm not much of a mechanic at all, so I just drive the 05 GT Mustang and do good maintenance and hope it doesn't quit on me. As Peacock illustrates, there's considerable discussion and disagreement, even among Ford drivers, as to what exactly "MODULAR" means and how it relates to the various engines. I surely can't offer any definitive solution, despite having read many books and articles over the years about Mustangs and Ford engines.
My lack of mechanic's knowledge and ability relating to my 4.6L engine, therefore, actually does tie in to the original MS280 thread: according to the evidence presented here, the MS280 with its ability to sense and adjust itself might be just the saw for me. I keep my equipment, tools, and vehicles clean and well-maintained, but I've never been able to fix more than just very basic problems.
SawTroll
Information Collector
If you keep the air filter reasonably clean, there is no advantage of the self adjusting carb, I believe......
Btw, I believe Husky intodused one also, on the Jreds 2156, but I don't really know if it stuck......
Anyway, it should be a non-issue.
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Lakeside53
Stihl Wrenching
Not true... Fuel changes winter/summer/region; weather, altitude, sure - air cleaner, etc etc... and those are just some of the "static changes. The carb also adjust when the saw is in the cut...
Thanks for the info. I'm curious though...How does the IEM system sense changes in altitude, air filter pressure differential, and fuel alcohol content? Does the saw have sensors such as MAP (Manifold Absolute Pressure), exhaust oxygen, throttle position, or engine/exhaust temp sensors? I thought (guessed realy, as all I have to go on is the Stihl brochures and info from you 'in the know' folks) that it just worked off of engine RPMS and a fixed set of parameters.
Boy, I have been out of the loop for a while. I didn't realize that modern saw carbs (regarding the non-IEM units) had that many circuits (and an accelerator pump on a small 2-stroke?). Sheesh. I'm still programmed for the older (what I'd consider conventional) Tilly, Walbro, and Zama two diaphragm 2-stroke carbs.
It's indeed true that 'Change Happens'. I still contend that there's Advances, but there's also 'Change for the Sake of Change'. The fun part is knowing the difference.
Perspective I guess...
You are surely right, these carbs are different than they were years ago.
The way the IEM monitors things, is that the microprocessor in the ignition module is always monitoring RPM, so if the filter is clogged up, which would cause rich running under load, the module leans out the mixture to compensate. Many saws have had compensating air filters which would automatically lean the mixture if the filter was clogged, by limiting the metering diaphragm movement. This carb has the metering diaphragm vented to atmosphere. So by monitoring the RPM the module adjusts the mixture for the best RPM under load automatically for any changes in load, fuel, altitude, etc. It is a very elegant way to do the job without an O2, MAP, or other sensors.
SawTroll
Information Collector
:sword: :hmm3grin2orange: :hmm3grin2orange:
Just Mow
Don't touch my Willie !!!
SawTroll
Information Collector
Know who to pick your battles with. This is not the one you will ever win.
...didn't think so either, just for fun......:hmm3grin2orange: :hmm3grin2orange:
I am lonely here, as the Witch has gone to bed........
Lakeside53
Stihl Wrenching
heck, I was just trying to get the last word, but..
SawTroll
Information Collector
heck, I was just trying to get the last word, but..
You just did, didn't you........oooppppps....:yoyo: :yoyo:
ford832
ArboristSite Guru
Electronic controls
Not to put this back in to cars but it does relate.The early electronic controlled carburetors(feedback) were merely an attempt to get a carbureted vehicle to approach the efficiency of an efi system.It was basically a stop gap between the two.It was a plumbers nightmare of vac hoses,lines,switches,solenoids and the like that failed miserably.EFI was the cure.As for the fuel filter issue,many efi and carbureted filters share the same filtration media but the delivery system differs.On a carbureted system,the fuel is pumped from the tank to the carburetor and is burned.On most EFI systems(some new ones are single line)the fuel is pumped from the tank to the fuel rail.The computer determines the appropriate pulse width and the injectors open then close.The remaining fuel returns to the tank via the return line.In this system,a molecule of fuel can circulate through the system many times before being burned hence the need for a larger filter.In other words,for a carbureted vehicle to burn a litre of fuel,one litre passes through the filter.For a fuel injected vehicle to burn a litre of fuel,ten litres or more may pass through it.
Not to put this back in to cars but it does relate.The early electronic controlled carburetors(feedback) were merely an attempt to get a carbureted vehicle to approach the efficiency of an efi system.It was basically a stop gap between the two.It was a plumbers nightmare of vac hoses,lines,switches,solenoids and the like that failed miserably.EFI was the cure.As for the fuel filter issue,many efi and carbureted filters share the same filtration media but the delivery system differs.On a carbureted system,the fuel is pumped from the tank to the carburetor and is burned.On most EFI systems(some new ones are single line)the fuel is pumped from the tank to the fuel rail.The computer determines the appropriate pulse width and the injectors open then close.The remaining fuel returns to the tank via the return line.In this system,a molecule of fuel can circulate through the system many times before being burned hence the need for a larger filter.In other words,for a carbureted vehicle to burn a litre of fuel,one litre passes through the filter.For a fuel injected vehicle to burn a litre of fuel,ten litres or more may pass through it.
Just Mow
Don't touch my Willie !!!
...didn't think so either, just for fun......:hmm3grin2orange: :hmm3grin2orange:
I am lonely here, as the Witch has gone to bed........
Troll, I notice that when she is in bed you are here and when you are in bed she is here.
Do you two ever sleep together:hmm3grin2orange:
You know, every now and then you have to get your freak on:notrolls2:
XJWoody
ArboristSite Guru
