Part Five: Ignition Timing

[Mastermind]

We've covered the exhaust port.

http://opeforum.com/threads/part-one-the-exhaust-port.7279/

The intake port.

http://opeforum.com/threads/part-two-the-intake-port.7290/

And the transfer ports.

http://opeforum.com/threads/part-three-the-transfer-ports.7306/

And compression.

http://opeforum.com/threads/part-four-compression.7318/

So now let's talk about ignition timing.

Should we advance the timing?

How much?

How can we tell if it's too far advanced?

Will timing advance make the engine overheat?

Can too much advance cause the engine to run lean?

Will timing advance hurt me? lol

Kick it around guys........ask the dumb questions. Please.

 

[TreeLife]

A couple degrees makes a big difference, I've seen big blocks gain 100 horse from a slight advance.

A couple degrees at a time until desired results achieved.

You can tell if there is too much timing if you hear popping under load.

Too much timing can cause preignition or detonation in some cases.

That's all I got.

What is most desirable for an actual work saw?

What do you find works best for a race rig?

Nick

 

[Stump Shot]

In and of itself a timing advance does not as much good unless a expected rise in RPM is expected. So I believe it's part of the whole package and helps everything work together kind of a thing. As the faster an engine goes the more advance is required.

As a side note, I am working on a fast, simple, easy and accurate way to measure actual timing in a modern power saw(modulated coil). If proven correct and true, I will share it with all you guys.

 

[TreeLife]

I like this guy ^^^

 

[Mastermind]

I like this guy ^^^

We all do.

 

[Simondo]

With coils that change advance on start along with some that can store a extra charge to aid start up ( Dolmar MPI coil ) ...shouldn't that situation be taken into account ?

 

[Mastermind]

Keep bringing the questions guys.

Let's get some folks in here.....

 

[Simondo]

What situation could you create if you "significantly" change the flywheel position on the M tron and Auto Tune saws that gather information from flywheel position for the brain in the coil...( that last bit is a assumption ).

 

[Adirondackstihl]

Eh?

 

[Mastermind]

What situation could you create if you "significantly" change the flywheel position on the M tron and Auto Tune saws that gather information from flywheel position for the brain in the coil...( that last bit is a assumption ).

I'll go ahead and chime in on this one Simon.

As far as I know, neither the A-T nor M-T saws are advanced enough to actually alter ignition timing in response to changes in temperature, load, fuel supply, etc.

 

[XP_Slinger]

How can we tell if it's too far advanced?

Will timing advance make the engine overheat?

Can too much advance cause the engine to run lean?

Will timing advance hurt me? lol

Kick it around guys........ask the dumb questions. Please.

Little story. While cutting with @RIDE-RED 350r s 394 barking in my ear a few weeks ago, my 372 developed what I thought was a lean burble during very long cuts. I ASSumed the saw was getting extra hot from the long cuts so adjusted the carb and went about the day. I cut with it last weekend and very clearly heard the burble (no 394 adjacent to me)and knew immediately what it was, too much timing advance. Haven't had time to reset the flywheel yet but I will before I run it again. I shaved about 1/4 of the key when I ported the saw and until now it seemed fine. I think the combination of switching to an unlimited coil with the filing advance gave it a little too much. The black coil does advance differently, when I changed it the idle was way off, it was like I was holding the throttle open just off the idle stop. Long story to say the sound and dogging down is a way to tell your timing is off

 

[sunfish]

I've heard 357s' like a little timing advance, but 346s' not so much?
Is something I've been wanting to play with on the 357s'.

Randy, do you advance timing when you do a 357?

 

[XP_Slinger]

I've heard 357s' like a little timing advance, but 346s' not so much?
Is something I've been wanting to play with on the 357s'.

Randy, do you advance timing when you do a 357?

I advanced my 357, no complaints. Improved throttle response IMO

 

[Mastermind]

I've heard 357s' like a little timing advance, but 346s' not so much?
Is something I've been wanting to play with on the 357s'.

Randy, do you advance timing when you do a 357?

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.

 

[sunfish]

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.

Odd, but Interesting.

 

[sunfish]

I have a 359 with a stock 357 top-end & is kind of doggie, not impressive at all . Think I'll advance timing a bit and see if it helps. Has 200 psi, but it really needs something else!

 

[Mastermind]

How do you like the one I did for you with stuffers?

Good? Bad? So-so?

 

[Simondo]

I'll go ahead and chime in on this one Simon.

As far as I know, neither the A-T nor M-T saws are advanced enough to actually alter ignition timing in response to changes in temperature, load, fuel supply, etc.

You have worked on them a lot so thats very interesting ....Stihl promo vid makes out that the system can change timing and fuelling which is why it got me thinking.

 

[Mastermind]

You have worked on them a lot so thats very interesting ....Stihl promo vid makes out that the system can change timing and fuelling which is why it got me thinking.

Notice I said "as far as I know".

I enjoy these type of threads because we all get the opportunity to learn. When I did the first M-Tronic saws I did not advance the timing because I thought the system was controlling advance. Other guys reported that they were seeing good results with timing advance on these models......so, of course, I tried it. They responded just as well as any other Stihl did.

So, I've come to the conclusion (right or wrong) that the system cannot alter timing beyond the retard that is built in the coil for easy starting.

 

[moparnut88]

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.

Well since you brought up spark plugs has anyone ever played around with different temp plugs with the modded saws. In the automotive racing we would play with our plugs temp depending on if the engine was na or turbocharged or even on nitrous.


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