Ignition timing hot and cold

[JimmyC]

In both my operators manual and my repair manual the static ignition timing is shown as 1-3 mm ATDC with the engine cold and 0-2 BTDC warm. I do not understand why it is different cold/warm nor have I ever seen this with any other motor. Does anybody know what this is about?

[rmel]

A bit of splitting hairs -- so to speak.

Lets say cold is 25C and hot is 100C. Then the centrifugal force springs
are going to have a lower spring constant at hot, and thus a bit more
advance. So they are compensating for cold vs hot springs.

Just ignore this. The advance for the Pinz is set for Alpine conditions,
high altitude, e.g. think Denver. So the advance is conservatively set low
and thus less than optimal unless you wheel at >6,000' all the time.

At 1,000 RPM set your advance to the higher end of the timing chart.
Then tweak it from there more or less depending upon your local and
how the engine runs.

[JimmyC]

Ron, but this is for static timing. Motor is not turning so the spring rate should not matter?

[rmel]

Hmmm... that's interesting. I go by page 24 section "O" of the repair manual.
I've ignored those cold/hot settings as being bogus. Although I have assumed
they were at idle as it doesn't say one way or the other.

The graph on pg 24 shows the desired advance vs RPM. At 900 RPM between
0 to 8 degrees. Which the mid point is not far from the hot setting. The pulley
diameter is ~162mm so there is about 1.3 mm/degree advance before the TDC
mark, or 6mm before TDC to be at the their recommended advance @ 900 RPM.

In any case, static is good for getting in the ballpark.
And except for high elevation even 8 degrees is on the low side.

[JimmyC]

If you look on page 22 it descibez the procedure and it is pretty purely static.

Also, I think the curves on page 24 are degrees of advance above static, not total advance, but they are probably close to the same.

I wonder if the factory timing was ping limited or max power. They spec 87 RON fuel which is like 83 (R+M)/2. If it was ping limited you could probably advance a bit and get more power with regular gas.