I timed the Atlas today

seattle##gs · Dec 18, 2018

still has the Lucas mag. Approx 34 degrees both sides. I think it still has the low compression pistons...what is the optimum timing?

texasSlick · Dec 18, 2018

The manual which came with my Atlas says 32 BTDC.

Slick

seattle##gs · Dec 19, 2018

I'm in pretty close, then. both sides are equal. If I close the gap a couple of thou then it should be on the money

texasSlick · Dec 19, 2018

Each 0.001 inch changes the timing 2 degrees in the same direction ... i.e. increase gap - increase timing advance. It is far more important to have gaps equal on both ramps, than to be spot on the specification.

Slick

acotrel · Dec 19, 2018

The amount of ignition advance depends on the knock-rating of the fuel and the compression ratio of the motor. Changing the advance can require changes to the jetting.

seattle##gs · Dec 19, 2018

I am lucky that both ramps seem too be the same. I am guessing that the compression is stock due to the relatively easy kick starting. There is no smoke when it starts up

nortonmark · Dec 19, 2018

seattle##gs said:
still has the Lucas mag. Approx 34 degrees both sides. I think it still has the low compression pistons...what is the optimum timing?

If still has dished pistons use 32 degrees according to specs, prop auto advance open, don’t forget to remove prop when done
Nortonmark

nortonmark · Dec 19, 2018

seattle##gs said:
I am lucky that both ramps seem too be the same. I am guessing that the compression is stock due to the relatively easy kick starting. There is no smoke when it starts up

They are and you only set timing on one lobe, the other lobe is automatically done from first timing point

acotrel · Dec 19, 2018

Why is the spec advance for a Commando 28 degrees and for an Atlas - 34 degrees - does it have to do with smooth running ?

texasSlick · Dec 19, 2018

acotrel said:
Why is the spec advance for a Commando 28 degrees and for an Atlas - 34 degrees - does it have to do with smooth running ?

The Atlas CR was limited to 7.5:1 to keep the shakes tolerable. The Commando raised the CR to 9:1 .... the shakes masked from the operator by the iso-mounts. I suppose the increased CR required the decrease in timing advance.

Slick

Bernhard · Dec 20, 2018

nortonmark said:
They are and you only set timing on one lobe, the other lobe is automatically done from first timing point

As some of us have learned to our cost about K2F magnetos don't take ANYTHING for granted. check timing with bulb and battery/ timing disc on BOTH POTS- everytime!!!!

texasSlick · Dec 20, 2018

Bernhard said:
As some of us have learned to our cost about K2F magnetos don't take ANYTHING for granted. check timing with bulb and battery/ timing disc on BOTH POTS- everytime!!!!

+1

If the gaps on both ramps are not equal, there is only one chance in a million the timing will be equal on both cylinders. That is called a 'fortuitous coincidence'.

Slick

johnm · Dec 30, 2018

Bernhard said:
As some of us have learned to our cost about K2F magnetos don't take ANYTHING for granted. check timing with bulb and battery/ timing disc on BOTH POTS- everytime!!!!

Yes !!!!!

One sides timing can be a mile out with respect to the other and you will melt a piston.

The error can come from worn lobes but also misaligned magneto shaft or cam ring. Anything more than 2 degrees between cylinders is not good enough. Split the difference between cylinders. I have seen over 10 crankshaft degrees differences.

I timed the Atlas today

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