Stihl saws kickback on starting

[CedChop]

Hi there, New to this forum but might have some info to help here.
It seems many have problems with Stihl saws kicking back on starting, hard to start or causing injury or at least shyness on new pull!!
Appears for some models like MS660 there are different later part number coils available that have ignition retard and/or advance built into the design (?).
Can relate to aftermarket ignition coils certainly affecting ignition timing, also the air gap between the coil armature and flywheel magnets is most important.
Too small a gap appears to advance the ignition timing although not by much.
One solution using the ignition coil that promotes kickback is to retard the timing.
Method: Its nothing fancy - a trial and error method to see what works for your saw in its condition, state of tune and with your starting technique.
Step 1 - Procure a timing light preferably an automotive strobe type using a 12V battery. Pull saw down to get at entire flywheel area.
Step 2 - Remove spark plug, fit up timing light to determine timing- use existing flywheel rim markings or make your own ink pen marks for a true TDC .
Step 3- Turn engine over slowly in normal rotation direction- use a drill or power screwdriver but not too fast to simulate pull starting speed. (Be mindful flywheel retaining nut may unscrew dont use impact driver.) Using strobe light , mark on casing where the ignition point is - relative to TDC mark.
Most likely this will be well before TDC hence the kickback tendency. Some of these problem saws are 20 degrees BTDC with this test!!
Step 4- Pull flywheel off, discard woodruff key. Retard flywheel position on crank, a small amount reassemble recheck timing.
Only a few degrees may be needed to stop kickback - sorry did say trial and error!! Try saw now on starting kickback tendency -no good go again.
Just prempting those against discarding the key- The woodruff key does NOT hold the flywheel in place ONLY aids in getting a reproduceable factory timing easily.
Tightening the flywheel retaining nut properly AND the flywheel will stay where its place forever. The tapers on the parts are self locking. Yes would be a better press fit joint without the keyway in the flywheel buts thats what we have to work with.
Welcome comments - try this out it will work just a lot of D and A required plus its hard to get timing "correct" again if flywheel is pulled.
Maybe someone reading this can tell us how to do that also how much retard works on which models?? Thanks for reading, Scruffy808

That all makes sense but what doesn't add up for me is that after about 4-5 careful slow pulls the problem goes away and its starting like normal. However, it does feel like a strong kickback pre ignition thing.

 

[Old2stroke]

Thanks Leaf and Old2stroke, appreciate your info. My project is Stihl 084, an old one. Her ignition did not make sparks so tried to fabricate another one on my own. This new unit works good so setting the timing will be next job to me.

Good job with that coil, not too many people would attempt to wind their own. Where I used to work at Canada's National Research Council, we had a coil lab with special winding equipment and a skilled technician to do the work. Easy job back then. Unfortunately all the modern electronic coils with a semiconductor package potted into the coil makes it very difficult to build your own for saws that require this type.

 

[chy_farm]

Good evening Old2stroke, and thank you for your comment.
Yesterday and this morning I tried three types, 15 degrees before TDC, 17 degrees, and 19 degrees. This last one gave me a couple of, not very big, but small kickbacks when I pulled the starter.
15 degreees, no kickbacks at all, but carb blows back more than other two, but this is only my presumption though.
Now she got setting at 17 degrees before TDC.
Here is a video showing experimental run.

 

[Old2stroke]

Should not see any difference between 15 and 17 deg and if you are going with fixed timing, anything less than around 25 deg won't give top high end power. Do you know what Stihl lists as the max. advance for that saw?
From the breadboard circuit, it looks like you have built your own electronic package to control the primary current in the coil, did that saw come with an electronic module or points/magneto?

 

[chy_farm]

Good evening Old2stroke,
I agree that a motor needs enough propagation time after it got firing, so propagation time less than 25 degrees is not enogh for a motor.
With understanding this, I yet do not like kickbacks, which gave me damage on my right fingers, jersey-fingers;
https://www.assh.org/handcare/condition/jersey-finger
Yes, I used a thyristor for a new CDI unit. This old Stihl did have an electronic module.

 

[Old2stroke]

Good evening Old2stroke,
I agree that a motor needs enough propagation time after it got firing, so propagation time less than 25 degrees is not enogh for a motor.
With understanding this, I yet do not like kickbacks, which gave me damage on my right fingers, jersey-fingers;
https://www.assh.org/handcare/condition/jersey-finger
Yes, I used a thyristor for a new CDI unit. This old Stihl did have an electronic module.

Sounds like you might have to use a circuit that will allow a lot of advance at high RPM but provide enough retard to bring it back to around 15 deg at low RPM (cranking speed). Did you do any searching to see if there is a coil for a similar model that could be fitted to your saw? There are many people on this forum that have a vast amount of knowledge and experience with Stihl saws. No compression release valve on that saw?

 

[Lightning Performance]

I have been modifying timing for many years in attempts to make non-oem coils work on various saws and my "ballpark" experience would say that timing at low rpm that gives up to 15 deg BTDC should not cause any kickback issues when cranking, once you get over 20 deg there could be some kickback but a lot seems to be dependent on the particular saw, many older saws with fixed magneto ignition were set close to 30 deg BTDC and didn't seem to have kickback issues. Just to clarify a point, electronic coils cannot advance the timing. The maximum timing is determined by the position of the FW magnets relative to the coil and TDC, the coil can only retard the timing from this point. To retard the timing the FW must be moved clockwise when looking at the FW. Of all the after market components available for saws, the coils have been the most frustrating, they seldom have a timing curve that matches the OEM ones.

Your wrong about coils. Now some coils do advance and retard timing in certain models.

MS 361 coil advances then ******* at higher rpms. It's a known fact.

Chy could be using anything he likes but should understand that timing curves are available for Stihl chainsaws.

 

[Lightning Performance]

Good evening Old2stroke,
I agree that a motor needs enough propagation time after it got firing, so propagation time less than 25 degrees is not enogh for a motor.
With understanding this, I yet do not like kickbacks, which gave me damage on my right fingers, jersey-fingers;
https://www.assh.org/handcare/condition/jersey-finger
Yes, I used a thyristor for a new CDI unit. This old Stihl did have an electronic module.

You have options for other coils unless you plan to stick with your new system with a thy setup.

One if my earliest 084s took out my hand a few years back for about two month because of kickback. It had zero to do with the stock two part ignition. The saw was dumping fuel in the crankcase when it sat. The first turns were ok but when it fired the saw wanted to kick back. This is a factory stock saw. No monkey business was done to it. Swapped the carb and had no issues since.

Enjoy

 

[Old2stroke]

Your wrong about coils. Now some coils do advance and retard timing in certain models.

MS 361 coil advances then ******* at higher rpms. It's a known fact.

Chy could be using anything he likes but should understand that timing curves are available for Stihl chainsaws.

Your wrong about coils. Now some coils do advance and retard timing in certain models.

MS 361 coil advances then ******* at higher rpms. It's a known fact.

Chy could be using anything he likes but should understand that timing curves are available for Stihl chainsaws.

Sounds like marketing hype, I’ll believe it when I see some engineering data.

 

[chy_farm]

Sounds like you might have to use a circuit that will allow a lot of advance at high RPM but provide enough retard to bring it back to around 15 deg at low RPM (cranking speed). Did you do any searching to see if there is a coil for a similar model that could be fitted to your saw? There are many people on this forum that have a vast amount of knowledge and experience with Stihl saws. No compression release valve on that saw?

Good morning Old2stroke. Tinkering chainsaw is not my job, it's my hobby, so digging deeper gives me deeper knowledge and makes my soul fascinate, this is only the reason I try fabricate my own sometimes.
Making examination on an old broken coil is also a fascinating project to me, to know e.g. if it has any electronic circuit, on oscilloscope (a pic here).
Next I see how a new capacitor works on a new board (a pic here too).
Then try a simulation on Spice to see final spark level (a pic here too).

Yes I tried to look for parts and found one on a site of used parts shop, my soul leads me to make new.
Yes this 084 has decomp valve.

 

[farmhard]

That all makes sense but what doesn't add up for me is that after about 4-5 careful slow pulls the problem goes away and its starting like normal. However, it does feel like a strong kickback pre ignition thing.

How well are your rings sealing?

 

[chy_farm]

--------- Do you know what Stihl lists as the max. advance for that saw?--------

Good evening Old2stroke, shame I overlooked this part from you. I wanted but I did not know it. Do you have this info in your hand?

 

[sean donato]

Sounds like marketing hype, I’ll believe it when I see some engineering data.

Kohler has systems that advance and retard ignition for years. It's nothing new in the small engine world. No reason to assume it's marketing hype in a saw.

 

[Old2stroke]

Good evening Old2stroke, shame I overlooked this part from you. I wanted but I did not know it. Do you have this info in your hand?

Congratulations on your perseverance in developing your own electronic package, makes me miss my electronics lab now that I'm long retired. Couldn't tell from the pics, have you succeeded in getting the right amount of retard? Sorry, I don't have timing info for that saw but for what it's worth, most of those older saws were set for max. advance of 27 to 29 deg. Use of the decomp valve allows you to pull the engine over faster and helps to reduce and tendency to kick back.

 

[Old2stroke]

Kohler has systems that advance and retard ignition for years. It's nothing new in the small engine world. No reason to assume it's marketing hype in a saw.

Those engines that had timing advance achieved it with some form of mechanical movement of ignition components, not through any electronic package in the coil as is found in chainsaws.

 

[sean donato]

Those engines that had timing advance achieved it with some form of mechanical movement of ignition components, not through any electronic package in the coil as is found in chainsaws.

No they did not. The s.a.m. and d.s.a.m. systems looked like normal coils more or less. Nothing mechanical attached to them whatsoever. Been standard on every engine for many years now.

 

[sean donato]

Then again, it's not like we haven't integrated other components like computers and sensors into the coils... oh wait thats called m-tronic.

 

[Old2stroke]

No they did not. The s.a.m. and d.s.a.m. systems looked like normal coils more or less. Nothing mechanical attached to them whatsoever. Been standard on every engine for many years now.

Will have to google those and see what it's all about. If they are that old, they should be points/magneto and most similar engines with timing advance had coils and points mounted on backing plates that rotated around the crank by linkage to the throttle control. More throttle, more advance.

 

[sean donato]

Will have to google those and see what it's all about. If they are that old, they should be points/magneto and most similar engines with timing advance had coils and points mounted on backing plates that rotated around the crank by linkage to the throttle control. More throttle, more advance.

The 084 was available till the late 90's I believe. most stuff that had spark advance didn't have linkage to the throttle, that's going back to the 60's - 70's possibly even older then that. Kohler introduced this with the ch family of engines. The spark advance went through many changes over the years, but still it was just a coil with a controller built in. Nothing new or exciting by today's standards. I'm sure Briggs and the like have similar systems. I got stuck as the "kohler" guy for my small engine i was responsible for right after starting at the machine shop in high school. So I didn't get as much exposure to other models till I was allowed to work on the diesel engines. Then eventually onto road work.

Edit: from what I can find the 084 was introduced in the mid 80's (85 but can't confirm)and went out of production in 97 when the 088 took its place. Not a saw that ever would have had a points ignition system. Not saying it had ignition advance, just it was an available technology of that time.

 

[chy_farm]

Congratulations on your perseverance in developing your own electronic package, -----------------------

Good morning Old2stroke, thank you for your words!!

----------------, have you succeeded in getting the right amount of retard? Sorry, I don't have timing info for that saw but for what it's worth, most of those older saws were set for max. advance of 27 to 29 deg. Use of the decomp valve allows you to pull the engine over faster and helps to reduce and tendency to kick back.

Now she gives almost no kick back to me, I greatly appreciate your tips here, many thanks.


But somehow she once in a while blow-backs from carb. I know this saw is not a reed-valve type, so if exhaust port was clogged with dirt/carbon, blow back could happen in the timing of overlap at the BDC. But her muffler was already cleaned before reassembly. Or a reflector plate placed just after exhaust port inside the muffler affects?
I altered firing timing to 17 deg., but I think this change has nothing to do with blow back.