Stihl Electronic Ignition - Gets Stuck In Full Advance?

[SteveSr]

Duly noted,dealer knows nothing then.

Sometimes Dr. Google is your friend!

 

[SteveSr]

Well, I looked through my spare parts and lo and behold found another "generic universal" Stihl IIDA Japan chainsaw coil. This one supposedly came out of an MS290 so it is probably about a decade newer.

Unfortunately, it acted just line the other coil. Tried to rip my hand off on several occasions. Apparently this is a characteristic of the type of ignition module.

I guess the only way to find out if it has static timing or running advance is to get a drill motor and a timing light.

 

[ZeroJunk]

Well, I looked through my spare parts and lo and behold found another "generic universal" Stihl IIDA Japan chainsaw coil. This one supposedly came out of an MS290 so it is probably about a decade newer.

Unfortunately, it acted just line the other coil. Tried to rip my hand off on several occasions. Apparently this is a characteristic of the type of ignition module.

I guess the only way to find out if it has static timing or running advance is to get a drill motor and a timing light.

I think (dangerous) the MS290 is a 0000 400 1300 and fixed.

 

[Old2stroke]

Well, I looked through my spare parts and lo and behold found another "generic universal" Stihl IIDA Japan chainsaw coil. This one supposedly came out of an MS290 so it is probably about a decade newer.

Unfortunately, it acted just line the other coil. Tried to rip my hand off on several occasions. Apparently this is a characteristic of the type of ignition module.

I guess the only way to find out if it has static timing or running advance is to get a drill motor and a timing light.

Yep, the easiest way to resolve timing issues is with a timing light, if you have a mechanic friend, he will probably give you his, as they are useless on modern cars. These engines with an electronic unit have to spin at a minimum rpm before they will produce a spark and this rpm is often higher than you would think necessary. I start slow and gradually bring the rpm up until it produces a consistent spark. Don't need a timing wheel to just check timing and it can all be done from the flywheel side.

 

[SteveSr]

I think (dangerous) the MS290 is a 0000 400 1300 and fixed.

I think that you are right!

 

[SteveSr]

Yep, the easiest way to resolve timing issues is with a timing light, if you have a mechanic friend, he will probably give you his, as they are useless on modern cars. These engines with an electronic unit have to spin at a minimum rpm before they will produce a spark and this rpm is often higher than you would think necessary. I start slow and gradually bring the rpm up until it produces a consistent spark. Don't need a timing wheel to just check timing and it can all be done from the flywheel side.

Actually RPM is a steady state condition. All the module cares about is the rate of change of the magnetic flux as the magnets sweep past the module. I think that this is likely why they can fire too early. The engine provides no resistance until the compression stroke by which time there is enough energy produced to fire the plug (too) early and try to rip your hand off.

 

[Old2stroke]

Actually RPM is a steady state condition. All the module cares about is the rate of change of the magnetic flux as the magnets sweep past the module. I think that this is likely why they can fire too early. The engine provides no resistance until the compression stroke by which time there is enough energy produced to fire the plug (too) early and try to rip your hand off.

And rate of change of flux is dependent on rpm. Many saws have ignitions that require a higher rpm than others before they will produce a spark and many coils are judged "bad" just because the operator wasn't spinning the engine fast enough in his test. I like a timing light as a spark indicator, the inductive pickup will only trigger a flash when a spark occurs, doesn't introduce an extra gap like testers do and you can see it in bright light and it will let you know if there is an actual spark during your normal start procedure. Regardless of why a spark could occur too soon, I have cured a few vicious "kick-backers" by retarding the ignition by 5 deg without any apparent (to me) degradation in top end performance. What puzzles me is I don't remember having this issue with any of the old saws with points magnetos. For instance, most of the Homelites from the 70's had high compression and fixed timing that was 28 to 30 deg and I don't recall having the cord ****** back, so either my arm was stronger back then or maybe electronic modules are doing something funny.

 

[SteveSr]

And rate of change of flux is dependent on rpm.

Correct but it is the instantaneous RPM (actually angular velocity) that matters and this will change (decrease) as the piston approaches the compression stroke and then increase after the power stroke.

What puzzles me is I don't remember having this issue with any of the old saws with points magnetos. For instance, most of the Homelites from the 70's had high compression and fixed timing that was 28 to 30 deg and I don't recall having the cord ****** back, so either my arm was stronger back then or maybe electronic modules are doing something funny.

I think that the electronic modules are doing something funny. Sometimes they pull over nice and just start. Other times they try to rip you hand off. So far my 034S is the worst but I have noticed this behavior on MS260/026 and 025/MS250s. The common denominator is that all of these saws use the "generic universal" (0000-400-1300) IIDA Japan coil.

I am now wondering what the effect might be of increasing the distance between the FW magnets and the module. The spec is .008"-.012". Theoretically this should reduce the energy available to spark at a lower speed.

I think that I have also noticed another idiosyncrasy in that it will fire early on multiple consecutive pulls. Turn the switch off. Pull one pull. Turn switch back on. Engine starts right up. Go figure.