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Timing Advance s- When \ When Not To Do - Questions

Greenthorn

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How do you all know when a timing advance will be beneficial?
Reading MM 660 build thread, I noticed he said "trial and error"
Is there really not more to it?
I don't mean that how it sounds, I know trial and error takes time and patience, qualities I am short on..:(.
Or is there really some mechanical timing numbers you're using?
I am asking and would like to discuss.
This topic is not about "me doing a timing advance."
Although I have done one on my MS261, and it worked great, I only did it because somebody told me I could do it and it was easy. Thank you Sir.
Is there some magic list somewhere that lets everybody know if they should "not" do the advance?
I guess I'm asking can we compile a list that says. "Touch or Do Not Touch!"
Or would every single saw made benefit from a timing advance?
I just wanted to hear what the masses know.
 

Greenthorn

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I can't remember where I copied this, but I thought it was very informative. If any of it is conflicting, let me know and I'll edit it for correctness.

Q) why advance timing?
A) By advancing the timing you are igniting the air/fuel mixture a little sooner.

Q) How does this give more power?
A) It takes time for fuel to burn so the spark always fires before the piston reaches TDC. In other words, the spark fires before the piston is finished with the compression stroke. What this does is gets the air/fuel mixture burning and close to maximum combustion pressure at just the right time.

Q) What happens if its not advanced far enough?
A) It fires too late and you lose power.

Q) What happens if its advanced to far?
A) It fires too soon and you get pre-ignition, and possible
sparatic engine rpms.
 

MustangMike

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A chainsaw motor is somewhat like any other motor. If you improve the exhaust flow, put on a less restrictive intake, or do any port work, likely a timing advance will be compatible with these changes. Everything has to work in sync to provide the best results. How much advance is a guess, but the normal 20/1000 off the key generally results in approximately 5 or 6 degrees, a reasonable amount.
 

weedkilla

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The golden rule of tuning is rich and retarded are safe, but no safer than correct tunes. Just safer than too lean and too advanced.
We don't have the advantage of adjustable timing maps, so all you can do is keep advancing the timing until the saw runs worse, then retard it to the least advance that gives maximum power. Then run the saw hot and hard and be certain you are still happy.
Just be aware that you can run into "too advanced" at any or all of starting, transition and full load.
 

Miller Mod Saws

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Here's 2 good senerios to help you guys out. The makita I showed in randys thread on the 7900 came to me with the 272xp coil mod. It would run but not well. It was blowing fuel out the muffler and would start but not well and would not idle. And would get hot in a hurry. When we do this particular coil mod our starting point is 30° btdc. I timed it and this saw was at 18°. I reset and rekeyed the flywheel and it runs like a champ. Now to port it. Next 7910 I kept advancing at about 36° it started getting hard to start and had started loosing power. At 38° it wanted to jerk the rope back outta your hand. Just experimenting. I've found the best performance to be in the 28 -32° range. Now this is with the 272xp coil mod. I'm not sure what I stock one runs
I should find out huh!
 

Homelite410

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ac0fe8ac17876d63222e19e07658c298.jpg
here is where my 350 runs. Its 21° iirc.
 

Miller Mod Saws

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Example #2. @Greenthorn this is for you. As a rule of thumb a little timing advance always helps. Well I find this not to be the case on a 6100 dolmar. I built the 2 in the build thread on AS. I noted I didn't see any gains but both saws were brand new so some run time was required. I took one of them to hedgefest. I just didn't like how it sounded. I can't explain it but @WKEND LUMBERJAK knows what I be talking about. I swiped some of Matts tools and took the 5° advance I had put in it back out. Not only did it sound better it ran better as well. So I guess I'm saying it's a lot of trial and error. Lol.
 

drf256

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Great thread.

How does one determine where 0* is on the coil firing?

What are you using as a reference point?

Is it when the magnets are in line with the coil legs?

I'm just trying to wrap my head around it as well. I've been advancing timing on every stihl I build.

On an MS260, I went from 20 to 30 off the keyway and the saw gained 500-1000 rpm with no other changes to the saw. The saw was fully ported though.
 

Homelite410

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Great thread.

How does one determine where 0* is on the coil firing?

What are you using as a reference point?

Is it when the magnets are in line with the coil legs?

I'm just trying to wrap my head around it as well. I've been advancing timing on every stihl I build.

On an MS260, I went from 20 to 30 off the keyway and the saw gained 500-1000 rpm with no other changes to the saw. The saw was fully ported though.
I simply used a timing light , marked a fin on flywheel, mark tdc as shown in my pic above, started the saw (warm), and removed the recoil cover. Trigger the light and mark where it flashes.

Just hook the light to a battery and to the plug lead.
 

drf256

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A timing light with advance can help alot, more like a boatload.
Just dial in the advance as you are running untill you match up the TDC mark, then read the light for total advance[
How are you guys starting a saw and flashing the flywheel?
 
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