Part Five: Ignition Timing

[drf256]

I got this over 20 years ago for tuning my 440 engine,it can advance and retard timing somehow when running ,looks like they used to have a 2 cycle adapter option ,wonder if would work on a saw ?View attachment 68859 View attachment 68860 View attachment 68861 View attachment 68862

Should work fine on a 2 stroke, I think.

That simply can read advance. I have the older style with a knob on the back.

I should be able to find TDC on the clutch and make a mark, then use my light to see what's what.

EDIT: I read it wrong. It appears you have a different contraption.

 

[Fruecrue]

Are there any trends? Rules of thumb?
Does a higher compression saw like more or less advance than a similar saw with lower compression?

Does a higher rpm saw like more advance than a lower rpm saw? Are there any exceptions?

Is there anything to be learned by lining up the magnets with the coil and referencing to TDC on a degree wheel?

 

[drf256]

I usually advance every Stihl .025 off the key.

The 262 can handle half of the cast key, which is nearly .050, with no problem.

 

[Stihlbro]

I want to say that most Stihl coils are full advanced some where close to 28 degrees. I use to use a degree wheel and mark/find the advance. 5 degrees always seemed to give that little pop at idle, throttle response seemed snappier and in my mind ran better. The stages of advance can vary, and trying multiple coils on a particular saw till you find the right one was common.

 

[Mastermind]

Ok that makes more sense now. I wonder on average what the timing retard is then b4 it goes back to the normal timing? 10* 15* or is every coil a little different. I could see where a 15* retard would be nice for big cc high compression saws during starting.


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I'm not sure......but 10 - 15° sounds reasonable.

I'd be interested to find a method of seeing what the actual timing advance numbers are for these coils. Can't hook up a timin light to them; so how can it be accomplished?

On stihl 041 s and other older saws that have a breaker plate a timing is shown hooked up to adjust and set timing
Connect timing light to a 12 volt source and attach the pick up to spark lead
Start saw remove recoil and you can see timing at any giving mark set stock then file key using same stationary mark check timing running
Its a reduced description of how to but i hope you get the idea




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Boom.

That's how I've done it. You do need a good timing light with adjustable advance to really learn from what you are seeing. Or, you can mark the flywheel.....

Are there any trends? Rules of thumb?
Does a higher compression saw like more or less advance than a similar saw with lower compression?

Does a higher rpm saw like more advance than a lower rpm saw? Are there any exceptions?

Is there anything to be learned by lining up the magnets with the coil and referencing to TDC on a degree wheel?

Higher compression coupled with more advance can break starter parts. More importantly, it can injure you.

More rpm would need more advance.....just simple physics I'd think.

Once you take the time to put a timing light on a saw engine, you might learn more about the relationship between the poles, and the magnets. I really don't know about that.

 

[junkman]

Should work fine on a 2 stroke, I think.

That simply can read advance. I have the older style with a knob on the back.

I should be able to find TDC on the clutch and make a mark, then use my light to see what's what.

EDIT: I read it wrong. It appears you have a different contraption.

On the car engines can push the bottom 2 buttons and find where the car runs the best with the timing light ,the mark on the crank actually changes where it is at with the light flashes ,once you get where you like how it runs ,remember where it is at and zero it back out and twist the distributor to where it was ,good for power tuning ,can test drive and tune for spark knock till it goes away on performance engines and know to the degree where it can be set ,not sure if they even sell this timing light any more,last 30 years of cars have scan tool options now

 

[Mastermind]

On the car engines can push the bottom 2 buttons and find where the car runs the best with the timing light ,the mark on the crank actually changes where it is at with the light flashes ,once you get where you like how it runs ,remember where it is at and zero it back out and twist the distributor to where it was ,good for power tuning ,can test drive and tune for spark knock till it goes away on performance engines and know to the degree where it can be set ,not sure if they even sell this timing light any more,last 30 years of cars have scan tool options now

That's cool.

 

[XP_Slinger]

I definitely need to figure out the magnet/pole relationship. My knowledge is so limited on that I don't even know when it fires the coil. Both magnets lined up with both poles? I would think so but that's a shot in the dark.

 

[Brush Ape]

If you widen the ports only without decking or cutting squish, what effect does a timing advance make?

 

[Mastermind]

If you widen the ports only without decking or cutting squish, what effect does a timing advance make?

It helps certain saws.......others it can still be too much.

Any particular saw?

 

[srcarr52]

I've found that most fire at 30-32 deg advance if you put a timing light on them.

 

[fossil]

Some really good reading here with regards as to how a magneto works and how and when the spark event is triggered.
Worth the read.
http://www.foxvalleykart.com/timing1.html

 

[Tor R]

First time I did advance timing was on 42 special, throttle respond improved alot, half the key is what I shaved, ruffly 6°.
All my 42's and 242's get a bit advanced timing nowadays, will try out the same on 254's also.

 

[Terry Syd]

I have this copy of Stihl's 'confidential' document on magneto ignition systems. It has a very good description of how everything is constructed with great pictures and cutaways. It also has a chart on the ignition advance requirements of a chainsaw through the RPM range.

Unfortunately, I can't copy any of it to the forum. Perhaps someone with more expertise could get the PDF file to load on this forum. I could probably send it as an attachment in an email to someone for them to give it a go.

Maybe one of the administrators could contact me via the forum private mail and give me an email address to send it to - then they could try to create a link for the forum members to use.

 

[Mastermind]

We will figure out how to get it posted Terry.

 

[Magic_Man]

I have.......but the gains are not real noticeable with the other mods I do.

This is gonna sound a little odd........but with a cut squish band the saw seems to need a little less advance. I've even wondered if the act of physically moving the spark plug closer to the piston crown isn't sort of acting as a timing advance of some sort.

Randy, my take on it is this. When we cut the squish band two things happen. One, we increase compression. Two, we improve flame travel in the chamber. We know compression makes the fuel/air charge more flammable and explosive. So it makes sense that a fuel mixture that's more explosive, and has a chamber design that the flame can travel faster would need less timing.

 

[Mastermind]

Randy, my take on it is this. When we cut the squish band two things happen. One, we increase compression. Two, we improve flame travel in the chamber. We know compression makes the fuel/air charge more flammable and explosive. So it makes sense that a fuel mixture that's more explosive, and has a chamber design that the flame can travel faster would need less timing.

I agree. Well stated.

 

[Stump Shot]

I think it could be quite simple. Have a wired remote electronic ignition system integrated into a control panel with two leads. One lead is a "pick up" for sensing crankshaft position and another connected to the plug. The control panel would have to be simultaneously running a dyno program.
So basically this would be an additional feature on a computerized dyno machine.

@wcorey

 

[wcorey]

@wcorey

I'm at best just a seat 'o the pants hack with the electronicals, learn as I go just enough to get the job done (or not).

It would be feasible to use most any old externally triggered coil and rig a pickup of some sort (optical, magnetic, hall) off the flywheel. Coil could be powered off the flywheel but chances are it won't easily adapt so you'd need a battery to power an external coil.
Then use any of a number of adjustable/programmable control modules available/intended for car/m'cycle use to adjust the timing on the fly. Or physically move the pickup, lots of options...
Integrating it into a dyno chart would certainly further streamline the optimization part. That would be Eric's @malk315 domain, but he's got more than enough on his plate with dyno stuff for the time being...

Problem with not having to adapt a coil and/or pickup to every different saw and using the stock self contained/triggered coils is that the SCR or whatever that triggers the field collapse event is potted in and you'd need access to that stuff to alter/interupt/replace it, typically not fun to dissect without mucking things up.
Best shot at real time adjusability short of replacing the coil with an externally triggered one would be a mechanical advance, like on those old outboards, physically moving the coil.
Saws don't usually have a lot of extra real estate to do that, some do though.
No simple answers...

On a side note, I've found in my travails of adapting somewhat more modern ignition systems (ike GM HEI) to older m'cycles that some types of very simple magnetic based pickup coils seem to provide an inherent advance curve as a byproduct more or less of their physics. As rpm increases, the triggering threshold advances along with it, some sort of 'effect' evidently.
I've also found that there is generally only a very small benefit to complex advance curves on basic engines as opposed to an almost immediate ramp up to full advance at relatively low (read starting) rpm.

 

[DND 9000]

I have this copy of Stihl's 'confidential' document on magneto ignition systems. It has a very good description of how everything is constructed with great pictures and cutaways. It also has a chart on the ignition advance requirements of a chainsaw through the RPM range.

Unfortunately, I can't copy any of it to the forum. Perhaps someone with more expertise could get the PDF file to load on this forum. I could probably send it as an attachment in an email to someone for them to give it a go.

Maybe one of the administrators could contact me via the forum private mail and give me an email address to send it to - then they could try to create a link for the forum members to use.

@Terry Syd
Simply use the upload a file button here in the forum when you write a message. It`s really simple.