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

[Brewz]

Ok so sounds like its best to run it where its timed the best and just tune it to the bar and timber

 

[mdavlee]

Ok so sounds like its best to run it where its timed the best and just tune it to the bar and timber

I did. 13k or a touch higher milling. 13.8k for cross cutting.

 

[drf256]

On the subject of the timing light, I think you're all correct for different reasons.

The plug fires when it fires and triggers the light, 2 or 4 stroke.

But the electronic circuitry in the light that calculates advance and changes the timing when the bulb lights likely would take 360 or 720* into account.

After all, why would there be a 2/4 stroke selector if they were the same?

 

[Moparmyway]

After all, why you'd there be a 2/4 stroke selector if they were the same?

The only difference that I have noticed is the rpm reading. I haven't perceived the light change, but I haven't looked for it either

In my mind, if Your correct and The light is on 4 cycle and I time my v8, I'm @ 72 degrees advance and not 36 .......... All my years at Atco, WestHampton, and Englishtown with nitrous and other power adders, I should have blown up every car

I'm fixxing to see Sunday before I head out for some cutting

 

[Al Smith]

As a reference the advance on most McCullochs is 26 degrees,most Stihls it's 27 stock .Lombard al -42 was 30 back in the day .

They say the lower the compression ratio the more some advance helps .

Some Stihls have self advancing coils,some don't.So trying to add more probably wouldn't solve anything.Make them hard to start if anything .

Back in the day they used to sell offset keys for kart engines and some used them on reed valve Mac saws .One of my 125's that came from Oregon has a 2.5 degree offset key .

 

[merc_man]

What about for testing perposes could you just take the key out and turn wheel a couple dehrees at a time till ya get the sweet spot or determine advance timeing dont help. And the file key way or would the flywheel move.

 

[Brewz]

It may not move but would not be easy to move in accurate increments of a degree or 2 for testing without the key as a stop.

I think the best way is to get a key, take a bit off at a time and measure as you go.
When done, start with a fresh key and cut it to the optimal amount found for your saw.

If slowly advancing timing like this, how would one recognize what point is optimal?
What are the first early signs you have gone too far?

 

[MustangMike]

I only take 20/1000 off an 80/1000 key, or about 1/4 of the key. I'm probably being conservative, but by my calculation that adds approx 5 or 6 degrees, which is about all I want to add.

 

[MustangMike]

It may not move but would not be easy to move in accurate increments of a degree or 2 for testing without the key as a stop.

I think the best way is to get a key, take a bit off at a time and measure as you go.
When done, start with a fresh key and cut it to the optimal amount found for your saw.

If slowly advancing timing like this, how would one recognize what point is optimal?
What are the first early signs you have gone too far?

The trouble is, on any given day, optimum may be different, so I would not want to go too far on a work saw. Likely, w/o a dyno, you won't notice much with 2 degree movements.

None of my saws are race saws, I just want them to perform "good" every day.

 

[Brewz]

Yeah that makes perfect sense!!!

Someone said in the thread I have running for the Stihl 066 red light said that the limited coil has 31* of advance as opposed to 27* with the unlimited coil.
For this reason I have left the timing stock and it has a different character to my 066 with the key filed about .025

It is harder on the arm to turn over, and if you disrespect it at all, it will rip your fingers off.
It also has a real face slapping crackly to it at idle. Like its angry.
Its louder than the unlimited 066 with identical muffler mod.

It does however, run like a scalded cat even though I cant lean it out. Its still 4 stroking solid at the 13500rpm limiter.

 

[Al Smith]

I can tell you from experience if you get them much over 30 degrees advance it will try to rip your arm off .The only reason those old time karters got away with much over than that is they cranked them over with a belt drive starter ,usually a long shaft Ford starter with a pulley .Plus the fact those old alkie/,nitro,castor oil burners idled at about 4000 rpm .--you can't do that chit with a saw.

 

[srcarr52]

Correct. Unlike the currently used "wasted" spark type simplified ignitions on most small engines these days, a dizzy is still driven 1:1 by the cam which is driven 1:2 by the crank. (1 being the cam, 2 being the crank)

But in talking about timing lights, it escapes me as to why it matters whether it is checking ignition timing on a 2-stroke or 4-stroke. Ignition is still occurring at X-degrees BTDC. It shouldn't care whether it's happening on the exhaust or compression stroke, or whether it is reading a 2 or 4-stroke... My timing light just hooks on a plug wire, then to the battery, and flashes each time the plug fires.. It doesn't matter if it's picking up a wasted spark on the exhaust stroke, the timing is still what it is. It doesn't change.

This only applies to timing lights that have an advance feature. The straight up timing light is just going to flash when the ignition sparks.

The timing lights with an advance feature have to calculate the time in between actual ignition pulses to spark. So therefore it needs to know how often in revolutions the ignition sparks. On the 4 stroke setting is expects every 720 deg on 2 stroke it expects 360 deg. If it doesn't have a setting then it's going to be on 720 deg, then to do a two stroke or wasted spark ignition you have to divide the number on the dial by two.

Here is my timing light, note the two sets of numbers on the dial.

 

[RIDE-RED 350r]

Thanks for the explanation.. I don't mean to sound ignorant, but I didn't know there are timing lights with those features and capabilities. Interesting.

So what does it do?? Calculate your all-in advance on an engine equipped with advance like a SBC without having to run the engine at the RPM required for full timing advance???

 

[Moparmyway]

This only applies to timing lights that have an advance feature. The straight up timing light is just going to flash when the ignition sparks.

The timing lights with an advance feature have to calculate the time in between actual ignition pulses to spark. So therefore it needs to know how often in revolutions the ignition sparks. On the 4 stroke setting is expects every 720 deg on 2 stroke it expects 360 deg. If it doesn't have a setting then it's going to be on 720 deg, then to do a two stroke or wasted spark ignition you have to divide the number on the dial by two.

Here is my timing light, note the two sets of numbers on the dial.

Thanks for the picture Shawn ! I've got 3 lights, all with advance, only one has a 2 stroke/ 4 stroke switch. I guess the other 2 I'd have to divide by two.
I didn't get to test anything today, made chocolate chip / M&M cookies with the kids ............. Priorities

 

[srcarr52]

Thanks for the explanation.. I don't mean to sound ignorant, but I didn't know there are timing lights with those features and capabilities. Interesting.

So what does it do?? Calculate your all-in advance on an engine equipped with advance like a SBC without having to run the engine at the RPM required for full timing advance???

No, it advances the light flash so you can set timing at full advance with ought having timing marks for 30+ deg. Set the dial and it flashes that amount before the actual ignition spark.

 

[Brewz]

I dropped into my local Stihl dealer today and ordered half a dozen flywheel keys for my 066's

I plan to keep a couple as spare unmodified, and mill amounts off 4 of them to be used for testing to find what my saws like.

I am thinking .010, .020, .030 and .040 cut from them.

Thoughts?

 

[mdavlee]

Probably wouldn't even try the .010". I go 1/3-1/2 of the key most of the time.

 

[MustangMike]

You may need to hook up to a dyno to see the differences, but it is an interesting test. I planned to do it on an 044 a while back, but never did. I just settled on 20/1000.

 

[Terry Syd]

Ozarker pasted in a good graph of ignition timing in this thread - http://opeforum.com/threads/limited-coils.2008/#post-91224

Check post #19

 

[Brewz]

Nice info Terry.

If that graph can be believed, that would explain why most find a good result with a simple .020 to .030 key shave to get advance up around 32 to 34 deg.

Here in Oz we don't often encounter cold starting issues, its more likely to be too damn hot to be out cutting wood, so starting them is usually not an issue.

I certainly never noticed any difference in starting then with the timing advanced