Probably 1/2-2/3 of the key on some saws.
The official CT Autumn GTG (07 November 2015)
- Thread starter Paragon Builder
- Start date
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Mastermind
Work Saw Specialist
You'll know when you've went too far. Most saws start breaking up in the cut when the timing is too high. I stay conservative on everything I do in the interest of longevity.
Won't your start to loose torque in the cut before you hit that break up stuff.
Mastermind
Work Saw Specialist
You might not Mike. I think you'll just reach a point that more does not help......then it starts acting up.
You may be right, but here is my thought process, the amount of timing for max strength at 14,000 RPM is greater than the timing for max strength at 10,000 RPM. Since few saws will maintain 14,000 in the cut ... well, you get the jist of what I'm trying to say.
So, I fired up 044 #1 today (the un ported one) after I gave it a 20/1000 timing advance. Had to lower the idle a bit, and it felt good. Just made a few cuts in a test piece of wood, but she felt a little more angry to me.
drf255
BAD CAD
Think of the old distributor curves. Back when the Sun machines were around to tune them.
I'm a Chevy guy. You want it all in by 1800 rpm for the whole powerband. And slightly retarded at the peak.
That may be what they did, but think of the purpose of timing advance, it is to keep the combustion process in sync with the RPM increase. The more you increase RPMs, the more timing advance you need.
14,000 RPMs is a 40% increase over 10,000 RPM. The optimum timing advance for both RPMs will not be the same.
It would be nice to see a dyno of different timing #s. My guess it that the aggressive timing #s will result in more power at max RPMs, but slightly backed off will provide more power at "in the cut" RPMs.
14,000 RPMs is a 40% increase over 10,000 RPM. The optimum timing advance for both RPMs will not be the same.
It would be nice to see a dyno of different timing #s. My guess it that the aggressive timing #s will result in more power at max RPMs, but slightly backed off will provide more power at "in the cut" RPMs.
I've done quite a bit of playing around with advance curves while adapting various electronic ignitions to old points systems on bikes and cars, as well as programmable/select-able stuff on more modern vehicles. From bench testing rigs to dyno time.
I've yet to run across a situation where the advance doesn't top out relatively soon in the rpm range and then run a flat line all the way up through to 'red line'.
OK, but if a saw is adjusted above that "flat line", it will likely not be apparent until it is under load. There is likely a small gap between optimum advance, and when the saw lets you know there is a problem.
Was that included in your testing? I obviously have not done the extensive testing you are discussing, so I will defer to you.
Was that included in your testing? I obviously have not done the extensive testing you are discussing, so I will defer to you.
I also imagine that fuel type and temperature would also matter, so going a bit conservative is likely a good idea (to give some room for changes). Air cooled engines have a wider temp range than liquid cooled.
My point isn't about what the the best number is at full advance but that whatever that number is, it seems to be good/stable over the majority of the mid/upper rpm range of the motor.
The ideal full advance number can obviously be affected by fuel, tuning, compression, temp, load, etc, only a couple degrees can be all the difference.
Not long ago I was testing various pickups to trigger GM HEI modules.
I noticed that the magnetic type pickups would cause the triggering event to advance with increasing rpm's.
After looking into it a bit, it seems that this is a known 'side effect'.
I wonder if these saw coils with onboard triggering exhibit the same effect, hence the 'auto advance curve'.
On an aside, another way to change ign timing slightly (on electronic coils) is to change the coil gap, less gap = more advance.
I noticed that the magnetic type pickups would cause the triggering event to advance with increasing rpm's.
After looking into it a bit, it seems that this is a known 'side effect'.
I wonder if these saw coils with onboard triggering exhibit the same effect, hence the 'auto advance curve'.
On an aside, another way to change ign timing slightly (on electronic coils) is to change the coil gap, less gap = more advance.
Wow, good to know, I did not know that (both items).
Thanks for sharing.
It is so great to have so many people with diverse fields of knowledge on this site.
Thanks for sharing.
It is so great to have so many people with diverse fields of knowledge on this site.
Mastermind
Work Saw Specialist
And that explains why opening the coil gap a few thousandths can help with the rope being snatched outta your hand on some saws.
malk315
Running Saws for Therapy
I learned very quickly to grab rope carefully with my MMWS saw -- serious compression on that thing but will never go back, running the saw is too much fun to worry about any tough to pull rope. When I get older and more fragile I'll have my kids start the saw for me 
drf255
BAD CAD
My wife starts my Masterminded 066 for me. Only way I could eliminate the decomp.I learned very quickly to grab rope carefully with my MMWS saw -- serious compression on that thing but will never go back, running the saw is too much fun to worry about any tough to pull rope. When I get older and more fragile I'll have my kids start the saw for me
She's great at baiting hooks too!
ri chevy
ArboristSite Guru
My first fire of the season.
ri chevy
ArboristSite Guru
I hope everyone has a Very Merry Christmas and a Happy New Year!
drf255
BAD CAD
Same to YOU and ALL!!!
