timing mod basics

[northmanlogging]

So the 064 is a bit of a dog good saw but not a skookum as i was led to believe.

So probably next weekend its going under the dremel.

I've ported a couple saws with moderate results. But never monkeyed with timing.

As i understand you just take a bit of the key stock but hos much?

 

[grizz55chev]

So the 064 is a bit of a dog good saw but not a skookum as i was led to believe.

So probably next weekend its going under the dremel.

I've ported a couple saws with moderate results. But never monkeyed with timing.

As i understand you just take a bit of the key stock but hos much?

Half the key, or so. Lots of posts on the subject, so research before grinding.

 

[Ketchup]

If you're porting the jug you change timing when you grind away the top or bottom of the ports and/or if you deck the cylinder and cut a new squish band. You change ignition timing by shaving the flywheel key. Normally the two are independent of each other, but they can result in a combined change. The fancy way to do it is to set a degree wheel and then mark a 6-8 degree advance. But there are a lot of opportunities for mistakes when setting up your wheel accurately, so most people just take a fraction of the key off and call it close enough. I take off 1/3, which is closer to 6 degrees. More than 1/2 the key will probably be too much and on many saws 1/2 is too much. Luckily you can add key back if you take too much by glueing thin slivers (strips of can work well) to the remaining key.
On 064s I think there are two different flywheels, one of which has two keys. Some saws have actual keys that are separate, but if I remember right these ones are molded as part of the flywheel. I would start with 1/4 to 1/3 removal. Older Stihls weren't as retarded as the newer EPA models. I like to mark the key with a razor blade before I start filing.
Let us know how it goes!

 

[Huskybill]

I’ve changed the port timing but advanced the ignition timing too so it kept up with the port timing. I took measurements of what the husky rep did on a 2100 cylinder and used his specs.

 

[trappermike]

I do not like to alter ignition timing in a saw(or any engine) until I know what it's factory ignition timing is BTDC to begin with stock,I check with a timing light and make corresponding marks on the flywheel and crankcase in a convenient and well visible place. Then with a degree wheel I create more timing marks at TDC,20,25.and 30 degrees BTDC. Then I can run a strobe timing light and see exactly where the factory timing is to begin with. Then when I make alterations to the timing I know exactly where it's going,no guesswork,I recheck with the timing light again. All professional engine builders do this ,whether it's motorcycles,V-8s or whatever,don't leave it to guesswork.

 

[trappermike]

For instance the timing of the old 275 Canadien (123cc) of 1963 was listed at 35 degrees BTDC.(way more than any modern 2-stroke)I thought wow that's a lot of advance on a 2-stroke,would incinerate any modern engine...Well remember this motor ran on 16-1 gas/oil mix,using #30 to #40 weight motor oil! With such a heavy oil mix in the gasoline that fuel-burning speed had to be incredibly slow,necessitating so much ignition advance. A modern gas-oil mix would cook it with it's stock advance . The hottest 2-strokes I've seen are about 25-26 degrees BTDC,that's where I go for basically to start. But I don't advance or retard timing before I even know where it is to start with.

 

[Ketchup]

How do you determine the stock ignition timing? Rotate from BTDC until the flywheel clunks past the coil?

 

[trappermike]

Well you really need a degree wheel on the motor,not such a scary thing,first find TDC,then make some timing marks,20,25,30 degrees BTDC and run a timing light. Find out the stock timing and go from there. In a motor like a 2100 I would want to know.

 

[Ketchup]

Okay, I think I get it. I put a light on the spark plug wire and then turn from TDC until it lights. That's the stock ignition timing. Usually between 20 and 30 degrees before TDC.

Shaving the key makes the spark happen sooner, so if stock spark was 25 degrees, then advancing it 5 degrees would be 30 BTDC.

Am I understanding correctly?

Honestly, I rarely mess with the ignition timing on Husqvarna. Usually it's on EPA era Stihls and they all seem to improve with a 4-8 degree advance. I can mark that without even bothering with TDC, so I never went deeper. This is very helpful.

It makes me curious about mix ratios. Is there information on ignition speed for different ratios? Would 32:1 need more advance than 50:1, or are they too similar to make a difference? Would more advance be needed for 91 octane rather than 110? You've got me thinking now. Thanks!

 

[trappermike]

On a low performance engine you can get away with advancing the timing from stock,not too much cylinder pressure,but in a high output 2-stroke,over-advanced timing will cook the motor very quickly.
Well if your mix is heavier in oil it will burn slower,needing more ignition advance.